Hardwood floors take a toll on knees, for one thing. My brother had a 15+ year professional career and can't sit for very long (plane, cinema, etc) without needing to extend his leg. And that's after missing almost no games in-season through injury; it just built up over time.
Or mat vs hardwood. I have a friend who practiced savate for years on hard floors (rural kid, we had no money for full equipment at the gym, also savate is practiced with shoes which are often forbidden on mats) and he said recently that one of his regret was not insisting to train on the judo mats/tatamis, and not because he fell often, but because it ended up straining his knees.
