Because its not in the bible. And the bible is true because it says so in the bible. Problem? (Insert trollface).

plenty of christians believe in evolution and the big bang theory.

Because most of them are uneducated.

Evolution contradicts Adam & Eve.

If evolution is a fact that means no Adam & Eve, no Adam & Eve means no original sin, no original sin means no need for the crucifixion and resurrection of Jesus.

The evidence that supports evolution also contradicts Noahs ark and the world being under 10,000 years old.

Edit: This is from the point of view of a christian who literally beleives in the creation story, I know plenty of christians see it as mostly metaphoric and believe in evolution and the big bang.

for the "core" Christians it would require admitting that the bible is not infallible which is a belief they want to hold onto.

Actually, I think mostly all Christians in the western world do accept evolution. The Catholic Church also officially accepts evolution.

The Christians who do not accept evolution, don't accept it for the same reason that any non-Christian who don't believe evolution wouldn't accept it - it is a matter of not being educated about evolution. I would say that nearly 100% of (if not all) liberal Christians accept evolution - I also think that the majority of Christians in the western world are liberal Christians.

I also feel that the atheist perception that all Christians don't accept evolution is a product of neo-atheist prejudice/ignorance.

(1) It was definitely a large but local flood if there was one, but a few christians beleive the story literally happened exactly like that (minority, I know), so that's just another possible reason they may have rejected evolution. But we know for a fact there has never been anything close to a global flood. The reason why a lot of these myths get passed on is not because it happened and many cultures experienced it, it's because of plagiarism, Noahs ark is just another example of this type of plagiarism.

(2) Sure, you could say that, but I was just speaking from the point of view of someone rejecting evolution, and reasons why. I was assuming this person took the 6 days literally, and believed the bibles dates.

(3) I don't know where you live or what experiences you've had being taught evolution, but I've never seen it being jammed down anyones throats so I can't really speak to that. 

Oh ok I get what you're saying, but that would be stating claims and not presenting evidence. See we have very reliable evidence for all that you said there, now if we could explain what evidence to people who aren't scientifically literate (me and you), people would believe it. This has been done plenty of times, Carl Sagen is perfect at it. 

I was told of some dude who's preacher told him that dinosaurs didn't exist and that what they had in museums were made of plastic and that is why they don't let you touch them plastic dinosaurs.

You can't honestly think that -- Christianity is the largest religion in the world with 2.1 BILLION people (Source)

Why aren't there 2.1 Billion people out there (One third of the entire planet's population) protesting evolution?

Because the overwhealming majority of them believe and trust in science. It's a small fringe group who doesn't -- but that small group is LOUD. The loud, very vocal minority of every group always make the rest of a group look bad.