Most people preached the benefits of rooting make a very compelling case. And often this case is to very dumb people. Dumb people like to complain. Loudly.
Remember from their perspective, 99% of all the feedback they get back (that they don't have to pay for) is negative. Therefore, they are solely concentrated on reducing that negative feedback by preventing failure in the first place. They view these protections as a way of doing that. It reduces the need for a larger support department and therefore their bottom line.
Of course, this ignores the fact that by making the methods for circumventing these protections more complex, they are creating a more error-prone process, and therefore a large support volume. But whatever, I didn't say it had to make sense.