All the local branches for all the rental companies are allowed to give out cars less than full because they do pick up service. Enterprise started this, so everybody copies it.
For instance, when I did the Hertz FL driveout, my car was by definition an airport car before, and so had to be returned with a full tank. At return, I overheard a conversation with the manager arranging for several customers to be picked up. The employee assigned to this task sounded like he was planning to use my Cobalt as a fuel-efficient customer shuttle until re-rented or the gas reaches half. The manager stopped him on his way out the door because there were problems processing the return thanks to incompetent MIA's computer goofups. The manager told him to take the Camry while my problems were sorted out.
So, this is part of smart business planning. The difference is that local branches for everyone else half a limit of half a tank. Enterprise doesn't seem to have one, giving me several cars in the past with the gas light on and the dashboard message center dinging.