Assuming this is the reason, it seems much less trivial to install more/better cameras in a store than to coordinate this effort.
I think you'd be surprised how hard it is to cover 100% of a store floor. As another commenter pointed out, even if you can angle matters. Getting a shot of the top of someone's head is a let less helpful than getting a good angle of their face.
And it gives more context to law enforcement when they can see faces, body language and hear words rather than hearsay.