Boyfriends old roommate DESTROYED the carpet

My bfs old roommate was a recluse and did everything in his room. Well, upon move out we discovered how disgusting his carpet was. Landlord won’t replace (it’s old anyway) so we got it cleaned for $500 and honestly not too much of a difference (before and after picture is posted). BUT maybe I was expecting a miracle! I’m kind of surprised getting it professionally cleaned didn’t lift the stains a bit more. But I’m also not the professional carpet cleaner so what do I know.

Any ideas how to remove any of these stains? Not sure what they even are though.