This kind of thing comes up a lot in discussions of operating systems, and while you and I might want to get "under the hood" the majority of users never want to do that, and know they don't know what they'd be doing if they got there. And accept that a sealed system might be safer (more secure) for them. Being able to maintain it yourself is a benefit, but having to maintain it when there's another maintenance-free option is unappealing.

Hence UNIX (of a sort) is actually quite popular on both iPhones and Android - but not in ways accessible to the user. Even if you do have to replace Android devices every few years because the manufacturer won't maintain them either.