It's really not difficult to get an unlocked phone in the US. This story kinda makes a mountain out of a molehill. I always get unlocked phones directly from Apple and just swap the sim or lately activate an esim.

Providers lock their phones bought through them because the vast majority of people in the US finance their phones through the provider. They simply don't want people financing phones then selling them and not paying the bill. Retailers like Best Buy do this because they're basically just middlemen for the providers. You can't buy an unlocked iPhone at Best Buy for example, all they sell is locked.

I've never heard of this AT&T taking ownership thing of unlocked phone, but one thing to note: don't everget AT&T at all. AT&T is probably the most expensive and at the same time useless provider. I have no idea why anyone has them except people like my dad who have never changed provider since he got his first cell phone in 1994 (Houston Cellular -> Cingular -> AT&T), I wouldn't be surprised if he was on some $240 for 2 lines and 5GB of data plan, he's that kind of person. Those are the only people I know who actually have AT&T.