>iPhones don't segment anything, yet they are locked tight.
Of course they do. There's market segmentation between iPhone tiers, between just using the iPhone as a computer (connecting it to a monitor and running macOS on it), differentiating iOS from the much less tightly maintained Android ecosystem (for which "walled garden" is a feature felt as "less hassle, less malware, more secure, mostly just works"), and several other things.
Apple would have liked to lock down macOS, but it's just not feasible (for now).