Cats can’t talk and even if they could, they’d probably still ignore most humans who they deem unworthy of their presence. Still cats need a way to communicate their feelings to their human owners, so one way they do this is through the litter box.
Many cats will stop using a litter box as a way to communicate to you their feelings. If a cat suddenly stops using a litter box, that could mean the cat is upset about something or simply messing with your mind. In any event, it’s still a form of communication even if you don’t like it.