Maybe because the same user who broke things on the computer is locked out on the phone/tablet so they can't break things. If it's broken it'll either be hardware issue or a firmware/os/app problem that has to be solved by the maker/developer.

In my experience supporting users of PCs, Macs, and Android and Apple phones/tablets, very few users have any desire for root access or any idea what to do with it when they have it. Their device is going to belong to others no matter what, maybe it's better for it to be Apple or Google or a somewhat vetted developer in a walled garden than the owner of a malicious bot-net.