Why are pet stores allowed to have such a horribe quality of life for the animals?

This is especially evident in fish as all the tanks are usually overrun with algae and snails and the fish all look sickly. Today i was in petsmart and saw a very large fish in the same tank as fiddler crabs with only about an inch of water. I’ve always wondered why is it they are allowed to operate giving such poor conditions to the animals they sell. I am in no way all PETA hardcore animal rights but like come on.