There are lots of unenforced laws. In Texas, there actually is a law prohibiting customers from taking carts out of stores themselves. This apparently was to keep customers from doing what they often do, taking them far from the store, and either dumping them or using them for their own tasks, like holding firewood in the backyard. Additionally, in spite of all the "[store] is not responsible for damage to cars" signs posted in parking lots, they really are liable for damage done by their equipment. So if only store employees take them out, the store can be sure of the carts returning.

But stores found out it's easier to let guests carry out their own things. And it's cheaper, since most people believe the signs in the lots, or decide it's not worth the trouble to go after the stores. Those few who complain may even get their car fixed, if they complain enough.