No console will sell more than PS2. The PS2 sold so well due to the large number of third party exclusive games it had. If you wanted to play a game, even a third party game, you had no other option but PS2. Now third party exclusivity is very rare, when it happens it is timed exclusivity (usually 1 year). Also it was the cheapest dvd player on the market. But now streaming is becoming more popular than buying movies in Blu-ray.
PS2 was not the cheapest DVD player on market. When the PS2 launched in 2000 for $299, you could get a DVD player for $100-$150. By the time it dropped to $179 in 2003, you could get one for $50. No one bought the PS2 to play DVDs. They bought it to game on, and then bought DVDs because it also had that feature.