For most iPhone users, the iPhone is their only Apple device. Maybe a few have an iPad (about one in 30 or so), but that's it. Most don't have a Mac, HomePod, etc, and so the "seamless ecosystem" is not a factor.
Talk to any teenager or young adult. It really is the green bubbles.
People care less about their computers/PCs. That market has peaked over 10 years ago and has been on the decline ever since, minus the temporary pandemic peak, while they are far more emotionally attached to their computer in their pocket (their phone) rather than the computer sitting on the desk at home.
Plus, computers being more open means you can do most of the stuff on a PC that you can do on a PC, it's very little you can gatekeep in that market software wise.
So Apple has "fixed" that "mistake" and not allow the iPhone to be nearly as open as Macs were, therefore more easily gatekeep features valuable for social interactions and keep customers tied.
But those same kids will have an iPhone, Watch and Airpods which also let you show off very visibly that you're in the Apple ecosystem when you're in public.