Comment by gogurt2000

For price and efficiency reasons you end up with 1 battery that's rectangular in shape. To maximize the capacity of that battery and minimize how thick the device is overall, you make the main PCB long and thin to sit next to the battery inside the case (instead of layering the PCB and battery).

That means your PCB runs along one of the edges of the device. You really only have 3 options for where to put the camera: in a corner along that edge, in the center along that edge, somewhere goofy between a corner and the center along that edge.

I would pick the corner because that's where people hold things the least. If you put the camera near the center and on the edge, then people are going to get their fingerprints all over the lens when they pick it up and hold it. It might be a little harder to aim the camera, but learning to work around that will be less annoying than learning to not touch the camera when you pick up the device or cleaning the camera every time you want to use it.

You could certainly put it in the center of the device, but to do so you either have to layer your PCB and battery (making the device thicker and making thermal transfer to the case worse) or you have to put batteries around the PCB and deal with the added cost and complexity of having more than 1 battery.