At least with most traditional marketplace content like prop models, you could reasonably expect that a marketplace asset is the exclusive property of the individual/business entity that created it. Sure, stock imagery can be incorporated into an artwork, but most of that action is limited to decal materials where common identifiers are found, like street signs.
If someone is ripping off your game, it’s much easier to make a case with traditional assets that you own a license and the offending party might not.
Wild west indeed.