Monks don't hit very hard, but they hit a lot, which makes up for it. While you might fancy yourself a Batman-esque brawler, effortlessly shifting from target to target, you would only hit each target for a handful of damage each time. Are there any mechanical benefits to attacking multiple targets during the round rather than focusing all your attacks on one target?
I suppose it's the difference between being Single Target or AoE. You absolutely can spread out your damage if a situation calls for it, but if you can take out a target in one round, wouldn't that benefit your group more than drawing aggro on 4 targets?