Well, i'll bet for several years it was at a bar or entertainment center of some sort, getting played constantly while the owner stopped by once a month to collect the quarters and unjam the coin slots. The glass stayed on the whole time, and the game got played right up until it broke.
I work at Pinballz in Texas. If we didn't clean it on a ridiculously regular basis, Tron pro would look like that in a month and a half. Worse perhaps since the playfield is all white and light blue