I have a hard time going back to my PS2, cuz my system sucks. It caused my last game to freeze randomly in the middle of playing it. I don't know if they made the systems to last long, or I have very bad luck.

I think there's a charm and mystery to PS1 and PS2 games that PS3 and PS4 games don't allow for. The graphics being worse on the PS1 and 2 along with some games having a lack of voice acting allow your imagination to run wilder. The games focus more on the important game design aspects rather than trying to impress you with their technological aspects as well. Not saying there aren't PS3 and 4 games that don't do both, but those games just don't allow for much imagination in comparison.

but playing the game on the ps1 is better and more emotional for me^^

Persona 3 is amazing. Still need to pick up 4 sometime. The PS2 is great, not my favorite console but it's pretty awesome.

This is indeed also a huge part of it.

It just seems that these games where made with fun and gameplay as the nr1 factor.

Never played 3 but i do know persona 4 is amazing and can't wait for p5

PS2 games are always playable imo.

Well not all of them are " playable"hahahha 

It's important to emphasize the lack of detail as a positive factor in the older games as well.  You aren't being distracted by how good the game looks and in many instances your brain focuses on just enjoying the game rather than "oh it's not 1080p! The walls aren't gritty enough! It's not 60 FPS! The character models aren't realistic etc."  You're free of such notions.

It happens because of nostalgia and nowadays it is more about graphics. And the games at the moment may have that wow factor at first, but it doesn't have that long lasting playability with the games that you've liked before.

And we are getting old, hence our playing time is reduced as well.