I wonder if the mixed reviews of iOS 11 have led them to do such major overhaul. Say if iOS was responsibility of one software dev team, and they recently hired a new project manager to overlook iOS 11 development and release then I would definitely transfer that PM somewhere else in the corp along with QA guys.

For example that bug "typing the letter 'I' autocorrects to an 'A; with a unicode [?] symbol instead" might not be that big of a deal, but as we all noticed how such minute change had drastic ripple effect in entire Apple's ecosystem.