What's the problem?
Primarily, and in general, it is what many people consciously or unconsciously assume about the nature of a free service.
Growing up as most of us do in money exchange economies governed by supply and demand, it is tempting to look at a free service the way a billionaire might look at the menu in a restaurant, since if he is just ordering food for himself, the ratio of the cost to what's in his wallet is so disproportionate that it might as well be free -- he can order any amount of anything that will fit on the table and it doesn't matter. He doesn't even have to eat it. Who cares? All that matters is that he pays for his order.
Unfortunately, this is a very bad analogy. Taken to an extreme, it implies that something which is free must be in infinite supply -- just about the only thing this really applies to is numbers. You can have as many unique real numbers as you want. They are in infinite supply.
Information, at least in an appropriately digestible form, is not. For that reason, in order for an information resource to work most effectively, that resource probably needs to be managed one way or another. Part of the way this is done here is via closing questions, something users with a sufficient amount of reputation, and community elected moderators, can participate in. In the latter case it is a de facto expectation that they do so.
To understand this, we need to to first understand that we are dealing with a supply and demand economy, but money is not a mechanism used to structure it.
As is often the case, the supply side is ultimately the governing factor.
Everyone in the world may want ten cars, but until there are ten cars for each of them, this demand cannot be met.
A question is asked by a person, and an answer is provided by a person (in some cases, as in this one, it may be the same person). A phenomenon new or casual users may not be familiar with is the significant imbalance between the number of people who ask questions and the number of people who provide answers. This is the case here as it is, as far as I am aware, on every Stack Exchange site. Have a look at the profiles at the top of our leaderboard and consider the number of questions asked and the number of answers provided. Right now, here's what they are for the top five:
- joan: 1705 answers, 2 questions.
- goldilocks: 1373 answers, 24 questions.
- Steve Robillard: 466 answers, 4 questions.
- Milliways: 1111 answers, 36 questions
- Jivings: 137 answers, 10 questions.
Since it is very unusual for the same person to provide more than one answer to a question, it does not take a math genius to figure out that these are far from what the site average would be. While gaining reputation is most easily done by answering questions, this still does not explain why there is this extreme disproportion between who provides the supply and who provides the demand in the Q&A economy.
Speculating about that is beyond the scope of this question -- it suffices that we understand it is the case, as it illustrates the extent to which what I said earlier is true: Supply is the governing factor here.
That being the case, a significant issue for managing the economy is setting a bar on demand without raising our prices, if we consider "prices" to refer to the money we do not charge. However, if we think a little harder, it may start to make sense that the zero dollars you pay for service here does not equate to you needing to make zero effort in order to be satisfied.
Questions which are unclear because they lack information -- often because the questioner has not made sufficient research effort first to clarify for him/herself what that information might be, but also often because the aforementioned "billionaire in a restaurant" assumption equates to laziness -- place a disproportionate strain on the supply. Put another way, they usually involve greater demand on behalf of the questioner than can be met by the supply without imbalancing the economy. This is why we expect:
You make a reasonable effort to do some research online beforehand to gather some contextual information for your question. By "research" I mean reading pre-existing material, not asking someone to write some customized for you.
You make an effort to express yourself clearly, include relevant details, and be explicit about your problem.
Two of the most common examples of a failure on this last point are XY problems (the examples in that answer are excellent illustrations of exactly how bad questions place more of a demand on supply) and an attitude that could be summed up this way:
I don't have to explain the details of my problem because that will take too long and/or I prefer to share as little information about what I'm doing as possible. However, that doesn't mean I can't try and ask a question, just that instead of explaining a problem, I will ask for all of the possible explanations for a vague delineation of it. The ones that don't apply can be discarded and it doesn't matter because like a billionaire at a restaurant, I can afford to throw away as much food as I like.
Hopefully the extreme selfishness in this is obvious. To be fair, some people do not do this consciously, they are just inexperienced in the world of sharing technical information online.
Something I often recommend to people, although it is a somewhat long and rambling read (probably just looking through it for 15-20 minutes is enough to get the point), is Eric S. Raymond's How to Ask Questions the Smart Way. The original was written more than 15 years ago, when the context of "sharing technical information online" was primarily via usenet or mail lists. However, what you see before you did in fact evolve out of that context.1 Raymond was a significant influence on the embryonic development of the free2 software community without which the Raspberry Pi would probably not exist.
Why can't I just ask whatever I want and leave it up to other people to decide individually whether they want to answer it or not?
The option for users to downvote and close questions is partially that, with a significant tweak: We can decide no one may answer this question, at least until it meets certain minimum standards. Here's a few good reasons for that:
It helps us save each other's time by indicating this question as it stands should be considered a waste of time, or as I described earlier, something which would place a disproportionate demand on supply. You are not the only person looking for help, and to be fair, the people who make a better effort asking for it are given priority.
It prevents people who are eager to answer questions, but in fact do not possess the necessary knowledge to do so, from filling a void. A bad answer is not better than no answer.
For people who are new to the whole realm, it helps them to understand what they are doing wrong when they ask a question. Although this may involve some bluntness at times, it is ultimately a kinder policy than just ignoring them and/or setting them up for a "let the blind lead the blind" scenario (all apologizes to the visually impaired). While there may be a fine line between that and rude, this is a bit an eye of the beholder issue. When in doubt, err on the side of pronoia as opposed to presuming someone is intentionally trying to hurt your feelings.
1. There were some other steps in this "evolutionary" chain, and as with biology, newer is not always better and the old often continues to co-exist, usually because they fill different niches which is part of why Stack Exchange is explicitly described as not a discussion forum. It isn't a mail list either, but no one would mistake it for such. Mail lists, for those who have never tried to use one, are still in widespread use and you will often find answers there you won't find here -- if you can find the right list. Note they tend to place an even higher bar on demand than we do, whereas the bar with discussion forums tends to be lower, which is likely why much of of the "supply side" has steadily migrated to Stack Exchange over its ~10 year history, beginning with Stack Overflow, which is certainly now the undisputed, far and away, most significant place for "sharing technical information online" when it comes to general programming topics. Just in case you think I am trying to imply we have an analogous relationship to the Pi Foundation's discussion forum, I'm not and we don't ;)
2. Free "not as in beer" is a phrase coined by Richard S. Stallman, another (probably more) significant historical figure. This is sort of akin to what I mean by free "not as in a billionaire at a restaurant". Note that he and Raymond have divergent views on what the "free software community" is/should be about.