Even a large AAA game should be able to be cloned to a machine. You don't need to clone history, just use --depth to specify the number of commits you want.
Obviously a 20 year git repo with all commits is going to be massive, but you don't need that locally.
Also, it seems like it would be reasonable for a AAA game to version control assets separately from code.
Probably, but you want to version control assets too.
People usually mention git-lfs at this point, but that is always annoying to use in practice. There is also shallow-clones and sparse-checkouts, but these only mitigate the problem as there is no way around cloning at least one revision completely with git.
Obviously a 20 year git repo with all commits is going to be massive, but you don't need that locally.
Also, it seems like it would be reasonable for a AAA game to version control assets separately from code.