FWIW it is simpler because BUSL source can change to any license (including copyleft), whereas FSL can only change into MIT or Apache 2.0. So it goes from N possibilities to 2.

> Is there any functional difference between apache and MIT?

Apache 2.0 has an explicit patents clause, whereas MIT does not.

Better explanation here: https://opensource.com/article/18/2/apache-2-patent-license