anecdotal but i recently went to the doctor to get some skin lesions checked out and she took photos on a tablet to send to a dermatologist. obviously that's a niche use but stuff like that, also optical character recognition scanning, situations where it's going to be handy to have a larger view of the photo so you can be sure it will be usable.
arguably this would be a good reason to make things more modular, so people who do want/need the rear-camera on a tablet can slot one in, and people who don't can get something else or just nothing.