I still don't understand how Ps2 sold like 3 million in its first year with such a mediocre lineup. PS2 was truly a sales monster. Though it did have a lot of releases and some franchises were much more popular in the past.
Well, situation was quite different.
PS2 : launched way before the next Nintendo system, follow-up to the PS1 which was really sucessful with both players and 3rd-party publishers, and lots of game coming... and consoles not dead yet. + DVD playback, which was a big thing back in the days (even though it sucked on the PS2).
Compare that to the Wii U : first to launch, but 0 3rd party support, very bleak future even in 2012, few games announced (even for Nintendo).
And PS4 : launched 1 years after the Wii U, which is struggling, market moved to handhelds and mobile, 3rd-party support should be there but... very few games have been announced (3 games since TGS 13?), and western-focused console. Oh, and the PS3 is still getting lots of games, so yeah.
It's not THAT surprising the PS2 sold as much as it did, as players expectations were pretty high back then. My guess is, both the PS3 and Wii U launch dampened those expectations, which is why PS4 is getting such slow sales.