But creationism also includes the progression of life after Genesis (at least as I understand it). The bible does say stuff about how each species was created by god and then didn't change after that - so evolution, as an alternative view, is a valid opposition because it says that each species evolved and is evolving.
I think the reason that creationists attack abiogenesis rather than evolution is because scientists readily admit that they don't have a strong case for it, just a bare hypothesis. It is seen as the weakest part of the ToE, even though they are separate things, and therefore the part which can be easily overturned or refuted.
Yeah, this is all just my wacky take on it. Enjoy.
The Rock Hound