Because very few high schools actually teach evolution these days. If it's not a Christian teacher who doesn't believe in evolution over his religion, it's all the religious douchebags on the school board or the vocal ones threatening to vote out the school board if they have science standards which put a lot of emphasis on evolution. Add to that the fact that most school text book manufacturers design their textbooks based on what the school board of the state of Texas wants (since Texas is such a large state they don't want to lose them as a customer) and since Texas school boards usually consist of conservative Republican Christians, it's not surprising that when kids reach college they have no idea how evolution really works. They think that picture showing progression from a monkey to a man is literal truth, or else they tend to believe all the lies that creationists put out there. It's sad that in a first world civilized country that 46% of people think that evolution is false and creationism is true.
Christian apologetics is the art of rolling a dog turd in sugar and selling it as a donut.
