To be clear, I would love to be able to install macOS on any PC. As a former Mackintosh user, I'm not excited about drivers, but I'd love to see it nonetheless.
But pushing Apple to make iOS available on other phone hardware is a massive undertaking. iOS is developed for a very constrained hardware set. When you move away from that and the optimizations thereof, what's left? It's a major distraction, you'll either get a much worse experience on other hardware, or the general polish and performance of iOS takes a nose dive. I don't see why Apple would spend the money to support this the way it would need to be supported rather than leave.
But pushing Apple to make iOS available on other phone hardware is a massive undertaking. iOS is developed for a very constrained hardware set. When you move away from that and the optimizations thereof, what's left? It's a major distraction, you'll either get a much worse experience on other hardware, or the general polish and performance of iOS takes a nose dive. I don't see why Apple would spend the money to support this the way it would need to be supported rather than leave.