It really is that simple. Phone makers are ignoring the basics. The ~60mm width of the original iPhone was not an arbitrary design decision - it's how wide it needs to be to get your thumb across the screen without having to shift your grip.
i can get my thumb across a pixel 2 xl just fine. however, i cant get even 50% up it on the left side and 90% up it on the right side. i can reach the top of a 5/se no problem. height is the problem, not just width.
The width is almost exactly the width of a pack of cigarettes. If those marketing folks know anything it’s what to make something feel good in your hand.
The "marketing folks" had nothing to do with it, of course. "Marketing folks" make zero design decisions for Apple. Design folks make those.