It was also out for so long that it gave it plenty of time to end up used for cheap. It seemed like everyone had one laying around or in the closet at home by the end of its run, usually a slim one honestly.
DVD playback was huge when it came out. DVD players were still expensive so if you wanted one, it barely cost any more to get a DVD player that was also a PlayStation. Between that and PS1 backwards-compat, the PS2 was a bargain.
That's true with the latest consoles too, honestly. They are even better deals in terms of what you get. My Xbox one is nearing 10 years old and it still plays new games, it plays a lot of the older games if they've been ported at least (bone of contention I know it not being proper backwards compatibility), performantly runs all streaming services (can't be said about modern smart TVs), its a blu ray player, I have 5.5 tb of local storage on it, and I got it used for about the price of a modern game.