It's the system

Meanwhile...

On the continent of Mossvale, the dragon pseudo-gods, having retreated from Aether Isle in a not-so-graceful manner, hightailed it back to their homeland. They were facing a full-blown undead invasion, and their first order of business was to deal with these lingering undead pests.

Although roughed up by Xiao Hui and Arthas, the two dragon pseudo-gods were still more than a match for these undead scrubs. 

A few more pseudo-god level undead might have made things interesting, but unfortunately for the undead race, their heavy hitters were all busy brawling with titans on the continent of Tyrangar. No time for a Mossvale vacation, apparently.

Unsurprisingly, with three dragon pseudo-gods on the scene, the undead army on Mossvale was wiped out faster than free pizza at a college campus.