I have pretty small hands and I use a 6.7" phone with no trouble. (As a size reference, I can comfortably reach the frets on a 3/4 size electric bass or a guitar, but a full size electric bass is too big for me and I can’t play without moving my hand a lot more than you’re supposed to.)
I don’t disagree you may find it comfortable, I just genuinely don’t understand how you do it. I guess you don’t mind the shuffling around that comes with typing a button in the opposite corner of the screen, but I personally do. When holding my phone with one hand in a position I can type in and the phone just won’t slide down to the floor, my thumb just doesn’t reach the opposite corner of the screen without shifting the phone in my hand.
I think it’s a matter if habits mostly. After thinking about it more, it seems I almost always use my phone with both hands. With one hand it does feel pretty awkward and unstable if I’m trying to do something complicated like typing. I can use it one handed and it’s fine for something like scrolling through social media or controlling a music player. I also use a launcher (Niagara) that happens to be designed well for using one handed on a big phone (but that’s not why I use it).
It could also be an Android vs iPhone issue. I use Android, and the back gesture is really convenient no matter how you’re holding the phone. I’ve noticed that iOS doesn’t seem to have a back gesture, and the back button in a lot of apps is in the worst possible place for one handed use. I think there’s an overall trend in Android apps to put the most important controls at the bottom of the screen, but in my (admittedly very fuzzy) recollections of Apple apps, they seem more inclined to put buttons at the top.
Dunno if it’s really an Android vs iOS thing considering I’ve been on Android since forever before the last 3 months. But yeah it probably has to do with usage patterns, of how you use your phone. I barely ever use mine two-handed unless I’m typing more than a sentence or two. I mostly navigate and interact with apps more than I type.