i don’t understand the details of the various licenses very well, so i just went with MPL because it sounds like a “middle-of-the-road” license between the GPL and Apache extremes. i understand swift itself is Apache, but Apple also has tons of lawyers to help them make that decision, and i don’t.
that said, i agree forcing everyone to make their forks public is unreasonable. i don’t know how anyone can enforce that anyway, if a fork is private. i don’t expect people to publish every modification, if they were maintaining a fork instead of submitting it as a PR (way less effort) it was probably because it was very specific to their application and not something that would make sense in isolation.