One nice thing about free assets is that you would be able to modify and remix them. So you could take some existing model of a car, change the dimensions a bit, change the shading, exaggerate some of its features and get a cartoon car that looks completely different.
Another thing is that you would not have to reinvent the wheel each time. Sure, you expect the important bits of each game to be unique. But do you really care that the wooden crates or doors from one game are reused in another? Being able to take an existing model of something unimportant and tweak it to match your atmosphere would save a lot of pointless work.
Just having access to such a library would not stop a good game development team for making a creative, distinctive game. It would just save them from having to make a whole bunch of boring models of limited utility. They would still make all the core models--characters, exotic settings and so on--for each particular game.
Besides, I think game studios already share assets between similar games in their own lineup. This would just make the sharing global, giving everybody access to more material to start from.