From what I understood, the initial motivation wasn't technical, but related to Apple's practices around a closed app store and the 30% tax on every purchase. He explained it both on Lex Fridman's podcast at [1] and a bit on [2].

[1] https://www.youtube.com/watch?v=mzDi8u3WMj0 [2] https://world.hey.com/dhh/living-with-linux-and-android-afte...