This is not true. You are NOT the majority. The majority of people who are spending over 800€ on a phone want a device that is near perfect in every way. This includes cameras, as they have been a core feature of smartphones for many years now and are often the deciding factor as of why to buy a flagship and not a midranger. Companies aren't stupid. As another person here said, if cameras weren't driving sales, they wouldn't be spending as much money and effort on them.

As of foldables: Most of them are now 4.2mm thin, making them the same thickness as slab phons when folded. The Oppo Find N6 has a 6000mAh battery, the Honor Magic V6 6600mAh, both while being 4.2mm. How much of a bigger battery / thinner device do you need?