Skimming through the moderator only list of migrations I tend to agree that the main paths to migrate posts away are indeed SO, U&L, and EE. Superuser is is less common and is more or less on a par with Arduino, Robotics, and Hardware Recommendations. IoT has been a target three times lately.
It is however noteworthy that migration really is not ...
It is because the site is still in Beta. Beta sites can only migrate to their own meta.
Most beta sites have had this question asked at some time or another. There is a more general answer on Meta.SE .