There's several reasons I can think of for the aoe spam, I've never met a boxer yet, but it's probably what I'd do too.

Imagine you are a valient little alliance mage, you enter Galv's room and are confronted by 5 identical Shaman and a sea of totems. The rest of yuor team is unfortunately cave defending or attempting to deplete your resources as quickly as they ca whilst avoiding any possible actual game objectives, so you must face them alone (so painful death is inevitable).

The reasons I'd pick aoe over single target are:
1. Aoe doesn't get eaten by grounding totems, you'd have to do a lot of ice lances to clear the forest before you could even start trying to kill something.
2. Unless you vastly overgear the multi-boxer you probably don't have the capabilities to kill one before the others have a) healed it up or b) nuked you to oblivion. Aoe probably lets you do the most damage to the group as a whole before your demise, whether this serves any purpose depends on whether your team mates pull their finger out and do something useful (unlikely).
3. Instant aoes can't be earth shocked. Locking down of the frost school would not be fun or profitable for our budding mage.
4. Jumping whilst using AE is probably a throw-back from back when the range of AE was increased whilst moving, this got fixed a little while ago, but most people probably are in the habvit of jumping without really knowing why.
5. Gnome + Jumping + AE = Win
6. Standing still in front of the MB is probably not a good idea as it will make you an easy target, if you are doing a pbaoe you can try to be out of los to at least some of the toons.

4v1 is never going to end well for the one, so you might as well go out with a bang.