Maplestory M Meso made a few changes whose purpose would be to prevent people from using one MapleStorym ability to train (or boss).Things like adding cooldowns or requiring charge-up, effectively altering the playstyle of classes that used to rely on a single maplestory skill.
Some might say that spamming one maplestory skill daily every day is dull. So? The game has lots of classes which have to, or benefit from, alternating/chaining/combo'ing skills. Play one of these if you find the one-key classes dull. Individuals who picked the dull courses, presumably appreciate that playstyle.
Some might say that relying upon a single maplestory skill is idle. Provided that spamming one skill on class A does not get you some better rewards than varying abilities on class B (in terms of MapleStorym DPS or whatever else), why don't you let idle people be idle?
Finally, there's the dilemma of keyweighting. If it's possible to spam one maplestory skill all day, a stone could do it for you. But for this, there are other options, like forcing movement after some number of strikes. The game already has that, it merely must make sure all abilities are restricted in this way. There is no need to induce people into playstyles they don't enjoy, just to buy MaplestoryM Mesos prevent cheating.
Bottom line: Trying to induce the same alternating-skill playstyle on all courses is bound to alienate a huge portion of the game's players. I think it's a mistake.