Someone loves all those dumb omgpop games, so don't knock it! Lots of people like being healers in MMORPGs and nothing is a dumber, simpler mini-game than watching bars and hitting "HEAL" over and over for hours. (I'm not saying *I* like these things, just that lots of people apparently do because they keep playing them.)
Playing DPS in most mmos isn't much better honestly. The biggest difference is that instead of looking at your party member bars you target an enemy and press your single target rotation mindlessly, or multitarget one if there are more enemies. Healers have to similiarily react to AoE damage, but regardless the playstyle is more reactive. Tanking on the other hand range from the most hectic job to the most boring job depending on the encounter. It's sad really, but that's what the healer-tank-dps gameplay will tend to cause on some fights. Of course nowadays in general there's always the "run away from fire"-thing too for all classes.
But yeah, I agree, if you make a potentially very boring thing FEEL like it's interesting and important, at least some people will do it. I mean, seriously, MMOs in general are hugely repetative and essentially extremely boring if you strip down the concept, yet there are millions and millions of people playing them because the concept brilliantly makes it seem like it's fun and interesting (at least for a while)
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