Why the Yamis? Because they are awesome. They're evil, they know it, and they're good at it. Not to mention, each of them has a distinct personality different from the others, which makes them even more interesting and completely individual.
Another great thing about them is that they each represent a different element. Fire, water, earth, and air for the four minions of Akuno, while Akuno himself represents pure darkness and hatred. As for light, who knows what happened to the light... only Akuno knows.
Although, the most evil of them all is definately Akuno Yami. The other four would have done nothing without him. It is even questionable as to why some of his minions actually work for him...
