Personally, it's a bit like if I purchased a Mercedes but found that I could only drive it on certain pre-approved roads, subject to varying partnerships and licensing agreements. Someone telling me, "you can just buy a scooter" seems predicated on the assertion that they both belong in the same category of "means of transportation," but ignores the fact that they operate very differently in several ways. It also ignores the fact that I've paid for the Mercedes (and possibly invested time and money into skills and tools to repair it), and can't necessarily recoup those costs.
Fundamentally, it ignores whether freedom of movement should be infringed in such a way. One can currently sideload an APK on Android, but what's stopping Google from taking the same hard line as Apple?
Note: I am using the hyperbolic analogy above for rhetorical reasons; I don't think Android phones are perfectly analogous to a scooter. We use Android at work precisely because of Apple's lockdowns, and while I actually like the OS well enough I think I would find it frustrating on a personal phone.