maybe you went on different lines that the ones I'm using, but I never found the most of the stations clean. Or it's just still better than what you're used to (I don't have much experience with subway in other cities)
Vienna metro was even cleaner and slightly less sketchy than Paris, but that is also not a fair comparison in terms of size and demographics. The Delhi metro is almost equally impressive as Paris's in convenience but feels about as clean as Ottawa.
Most Indians gush at the cleanliness of the Delhi metro. It is a world ahead of most average India Rail cars and stations. (I'm not speaking of long distance, upper class cars. Those are amazing, but ridiculously expensive.)