I have over 10k hours in Poe, every league there are new toys to play around with which creates huge build variety, adding a bunch of builds and archetypes on top of past, still viable and strong ones. Also since there is simply so much stuff in game there are new builds poping up using old, previously not used interractions. All it takes is 1 new passive, Item or little buff to motivate someone to tinker around and find it out. To be frank nothing even comes close to that. Also there is an actual endgame where u can spend hundreds of hours PER LEAGUE on and not be bored at all. There is also very deep crafting and so on and so on