Or maybe it's just that building a kernel, network stack, etc from scratch, and getting it to the point where it's stable, secure, sufficiently performant, comp

Or maybe it's just that building a kernel, network stack, etc from scratch, and getting it to the point where it's stable, secure, sufficiently performant, compatible etc, compared to what's already out there is a massive undertaking - microkernel or not - and they just need more time. Let's not forget that Android didn't even have smooth 60fps scrolling until well into the 2010s.