I am asking out of curiosity and nothing else: what use cases do you have that motivate you to get a new phone every year? Do iPhones get notably better with every release? I'm guessing camera or storage would be big ones?

I'm not parent but a counter perspective - the only three motivations I have are: phone dies camera vastly improves (imo it's been on a decline since the Nexus 6) phone is too slow to use

I'm on year 5 of my Samsung s21u that I can replace the Samsung ux slop with asop ports

Well, with this last one they finally made the telephoto 48MP. Also, vapor chamber is nice. I don't know if the 18 will have enough for me to upgrade, and it might even have a reason for me not to upgrade (removing gestures from Camera Control). But so far it's been every year, because I've only been using iPhone for a couple years, and my first was a refurbished 15 Pro Max.

The 17 Pro (non-Max) only comes with up to 1TB of storage, but that's still more than my 15 of before.