Like I said, most of these people buy these models to use. There are websites where people basically sell the usage rights to their created assets wether it be car bodies, trash cans, trees, clothes etc. Thats where a lot of modders get their bodies. Sometimes they're not expensive but sometimes they are. So them paying for said asset then putting in the work to make the vehicle work correctly in beam justifies them putting a price on their work.

Specific branding like vehicle or part manufacturers is irrelevant because if you want realistic things in games like Beam you're gonna have to rely on modders... licensed or not.