I think part of the problem is that much of our laws and intuitions are built for a time when there were competitors or they are designed for local marketplaces rather than internet scale businesses.

If my grocer is a jerk, I can go to a different grocery store. If this mechanic is always giving me dubious advice I can find a different one. Modern businesses, at internet scale, really aren't that way though. They are much more "winner take all". Maybe there are one or two winners, but when they win they really do take almost all the market share. And for most of the developed world simultaneously.

I can kind of get my own phone. Someone else in this thread mentions Purism. I could also get a rooted Android phone and install a version of Android that takes out Google. What I can't do, effectively, is make my own app, if the duopoly would prefer I not. I could put my app in a private app store or offer it to the kinds of people who use Librem phones, but the market there is too small to run a successful business. Google (via Android) and Apple are effectively both a monopoly, they sell/control almost all of the phones, and a monopsony, they control almost all of the supply of phone users.