And that's why things slowly rot away. Cleanup should be a priority, otherwise it eventually slows down new feature work.

In fact, a project should not be declared finished until its inevitable follow-up cleanup tasks have been completed as well. Just like a party weekend is not finished until you have cleaned up the mess after. Somebody is going to have to do it, and if it's not you right after you're done with your deliverables, then somebody else will have to do it. Possibly yourself further down the road when you actually want to do something else more exciting. Just like doing the dishes. Nobody wants to start preparing a big meal by having to do the dishes from the week prior.