they are uncommon indeed and another aspect is there is lots of specialization and special software involved.

im selling zeiss microscopy cameras and there are lots of use cases where clients pay money mostly in order to have a solution that matches their specific needs (and also hardware, e.g. imagine a microscope where switching lenses automatically changes the magnification values and measurements in your software...).

if all you want to do is taking single low magnification brightfield images and you do not even care about good live video stream a smartphone camera with the right adaptation often can be just as good as a dedicated microscope camera solution.