Dunno what made me think of this just now. When I worked for IT in a school district way back in the 90s, a librarian told me she kept a supply of mouse balls in her desk because kids would steal them out of the school computers. What I remember about those balls was they picked up dust and crud off surfaces. Pretty soon optical mice came along and they were history.
I remember doing work experience at school in the computer lab. Thought I was gonna learn fun stuff on the servers, ended up cleaning gunk from the rollers if every mouse in the entire school (And cleaning every PC out, and flashing entire labs one by one with updates OS…)