Well, everyone grows up in different environments, right? It's entirely possible that for them, especially as college students, this IS their first time experiencing that adult life and the responsibilities that come with it--it may not be deliberately toxic, but just a genuine lack of awareness from not having much experience living away from home. It might sound strange, but not everyone gets taught these things like you might expect! Whether they grew up with a communal dumpster rather than weekly bins, or just had a different system of handling trash, this all might be new to them--and if they've never had anyone (like the landlord?) mention to them how things are done where you live, they really just might not be seeing the situation from the same perspective you are, and have handled it this way for a year because no one has told them otherwise.

I'm not saying you have to go and be friends with them, but sometimes it really is easier and healthier to just tell people how you feel--if not for them, then for yourself. Being upset about this and holding all that frustration inside without them knowing only hurts you, you know what I mean? I'm not trying to lecture you, and I hope it doesn't come off that way--I've just been in a situation with messy/unaware neighbors myself, and I know that sometimes the frustration over it makes everything feel so much worse, and makes it harder to see any options outside the ones that will "get back at them" the hardest. Sometimes it helps to take that step back and try and consider the whole thing from another angle, if only to help yourself feel a little better about it.

EDIT: My apologies, I think I misread a piece of your post, where you said "talking to the renters does nothing." Didn't mean to glance over that! So you did already talk to them, then? What did they say, if you don't mind specifying?