Because you suck, that's how! That angel was an interesting one though, they didn't actuall kill that one. They tricked it into coexisting with the Magi by making its only alternative to be death. But by evolve, I was referring more akin to human evolution, from one form into another. No matter what that Angel did, it was still a virus, just one that was lulled into become docile.
I'm going to sleep now, but everyone who loves Eva owes it to themselves to check out Nadia, in a lot of ways, its the blu-print for what became evangelion, plus 11 or 12 network contracted epsidoes, but that's another topic.