I'm still using an iPhone 12, and given I have a proper camera, see no reason to (ever?) upgrade. After a battery replacement, it still runs perfectly well. That seems like a problem for Apple.
I think the 12 was great, and the main driver when I upgraded to a 14 was much better stabilisation when shooting video. Otherwise I probably would've stuck with it.
Apple makes a sizeable sum through the App store and accessories. I don't think low churn on their flagship hardware is keeping their executives awake at night.
It's a problem Apple could easily fix: put out another small phone. I'm in the "cold dead hands" camp with our 13 Minis: when the battery dies, get a new one and hope Apple comes to their senses in four years.
OTOH, maybe the iPhone Fold will turn out to not be two giant slabs of glass that still won't fit in your pocket. Maybe it'll be a reasonable size folded up, and big when unfolded. A person can dream...