Usually it’s a combination of internal packaging and usability.

Inside a smartphone, a large flat battery takes up much of the back. A centered camera module can force harder design compromises, such as splitting the battery or redesigning internal components around the camera, which increases complexity. A top corner often has more usable internal space because other parts of the phone already leave less room there.

Ergonomics also matter. For many people, a corner camera is easy to keep uncovered when holding the phone in one hand. If the camera were in a different position, some grips could block the lens or make shooting less comfortable. In practice, the upper corner tends to stay clear during normal use.

Traditional dedicated cameras often have the lens centered for different historical and structural reasons, but smartphones are designed around very different constraints: thin bodies, large batteries, screens, and one-handed use. So a corner placement is often the most practical solution rather than an arbitrary choice.