If they don’t break/cease to function they just plain wear out.
I have lost count of the quantity of keyboards that have died under my not so gentle ministrations and looking at my current victim I see that several of the keys are worn blank.
O, A, S, N. H L. and the SHIFT key are either blank or worn away to a degree of illegibility.
I am not a touch-typist but fortunately do know the QWERTY key board well enough for it not to matter too much. But I suspect that very soon now a new sacrifice will need to be offered to my altar of communication.