Because consumers prioritize camera quality over everything else. It sounds stupid, because it is, but it is the number one quoted purchase factor in surveys, right above weight and screen size. Social media clout and influencer culture have made people care excessively. But the prime limitation to phone camera qualities is sensor size. They are tiny, they have to be. The larger the sensor, the larger the optics required for them to catch light properly. These are physical limitations that will never go away. If anyone wants better quality cameras, it means either bigger bumps on phones or switching to large sensor dedicated professional cameras. Any foldable phone is forever cursed to have a bump as long as people care about those big three.