Even that should be optional. I should be able to do with my device whatever I want to — including bricking it, deliberately compromising it (for whatever reason), and installing a different OS on top of it. Of course, there should be some sane defaults that prevent me from it, but if I really wished to, I should be able to do one (or twenty) deliberate action(s) that make that possible.
No control of what’s installed and what not means no control over the money
they make far more money from device sales than they do from apps. they just don't want to give up their gatekeeping power