Why do we play Maplestory?

Not a MMORPG
Not F2P but B2P.
Again:
F2P MMORPG.

Don't get me wrong I've quitted maple for like 4 years now, but I can't actually name a single F2P that doesn't give a huuge advantage to the players that spend money on it.

League of Legends if a F2P game that doesn't give a huge advantage to the players that spend money on it. Also, considering it's got a playerbase of several million who play in direct competition with each other, I'd say LoL is the perfect example of a F2P MMO that doesn't give huge advantages to players who pay. Whether you consider it an MMORPG or not is semantics, in the long run. I see leveling with a varied pool of (How many?) millions of people over the course of a single night while completing a singular goal as an MMORPG. You see instanced battles as something else (I guess). To each their own.

As far as Guild Wars 2 goes, the initial purchase price is nothing when compared with the actual, F2P model they use at ArenaNet. You have to drop a few dollars to get the game, but the F2P model keeps the game running.