Roommates want rent decreased over mowing the lawn

I (25M) live with 3 of my friends, Abel (23M), Ryan (25M), and Chase (27M), in a house where we all split the rent evenly based on room size. I’m the cleanest one out of all of us and I’m consistently doing house chores such as the dishes, sweeping and mopping the floors, taking out the trash and putting the bins out, etc. they always leave used pots on the stove, cans of their drinks everywhere, and generally don’t care about the state of the inside of the house. Just recently (3 months ago), we acquired a lawnmower and a weed whacker, and Abel and Ryan have mowed the lawn at an average of once a month.

They’re now requesting that if no one else can mow the lawn except for them, that they get their rent decreased. I told them no because it’s a household chore and I’ve never asked for a decrease in my rent for cleaning up after them, but they insist that mowing the lawn is harder than any of the tasks I do. I suggested that we make a list of chores that need to be done throughout the month and we can split them evenly based on difficulty, but I don’t think they’re OK with that.

You should also note that all of us are in college. I work a part-time job as well as full-time school. Ryan is part-time in school but works 40 hours a week. Abel doesn’t have a job and is only part-time school. Chase is usually never around, but he’ll make a guest appearance every once in a while as long as he pays rent, I don’t care what he’s up to. But I think noting this is important because since I’m a full-time college student, I don’t really have much time to allocate to chores since I’m consistently at school if I’m not working.

What do I do?

TLDR: my roommates are lazy and don’t clean up after themselves or do any chores. They’ve mowed the lawn three times and now they want a decrease in rent.