Help me understand what will happen to maple.

It's the same game. Or rather, a different game - different mobs, maps, skills, quests - but with the same concept.

The main reason for levelling is to acquire new skills. I don't know of any class where the core build is done by 100, everybody gets their "smexiest" skills in fourth job.
In the game today many classes finish maxing the really useful skills between 140 and 160, so you may well say there is no attraction to levelling beyond that.
This is especially true now with potential, which makes the few AP you gain per level almost meaningless compared to your gear.

I have not studied BB enough to say whether it provides enough interesting skills to motivate one to level all the way to 200 to get them all, for any class.

Most exploits I've seen, btw, are about money, not levels.

Money is in a distal relationship with leveling and stat whoring. You use money to get better stats (or buy more potions) to level faster.

The core of just about every 3rd job build is finished in the 100-110 region, just as the core of just about every 2nd job build is finished between 50-60. 10-30 for every job is the only region that seems just about right for getting all the necessary skills. Now do a little bit a of research on when people are more likely decide to quit the game because leveling seems just a bit pointless. There's much more potential for variability in deciding to quit after 120 (much fewer feasible training areas, expedition drama).