Why do we play Maplestory?

DFO (Dungeon Fighter Online), while it was still alive, was well done for a Nexon game. While its Korean counterpart is still going strong, the American port was doing fairly well. Here's the cash (NX) part.
1. Buying safe upgrades (storage) (Perm)
2. Buying dual skill build (Perm)
3. Pets (Perm)
4. Avatars (option of duration or perm) clothing for looks + gave stats especially the "rare" quality ones.
5. Keys (Gachapon)
6. kaleido boxes ( reroll quality which changes stats a bit)
7. (PSOK type item to allow tradeability on rarer stuff)
8. Bind cubes ( combine avatars for a chance at a rare or clone rare)

I think that's the majority of it. Only thing not buyable with the ingame currency was the keys/kaleidos/psoks/safe upgrades/ dual skill builds. You could get kaleidos and keys daily so really it was a quality of life kind of upgrades. Clone rares carried the stats of rare avatars in addition to allowing you to fully customize what you wear. So the rich used those and the poor would often use the sets Nexon would have for sale or just buy cheap ones.
Everyone had access to end game. The end game sets were also really good for that matter and were ONLY obtainable from the dungeons. Unfortunately with the lack of security that Nexon put out it did become completely overrun by hackers/botters.
Also the really good stuff wasn't tradeable, so either you got lucky and obtained it or you farmed for it.