My guess: dirt. With as few moving parts as they typically have, console controllers already experience durability issues for less... hygienic, players. With

My guess: dirt. With as few moving parts as they typically have, console controllers already experience durability issues for less... hygienic, players. With trackballs that issue is compounded, even if you make them easily removable so you can clean them (just having to clean them at all would be more of a hassle than people are use to).