From their point of view, they start with interpreting the Bible as literal as a default view. When we say that the world is actually extremely old and that all creatures evolved over a long period of time, that threatens their interpretation of the Bible. They feel that if they allow evolution to be true and shift away from that literal interpretation, they're abandoning the underpinnings of their faith. That's why they continue to fight against it when it's so obvious the world is not a mere 6000 years old.
I think they're stuck on the horns of a dilemma.
The only way they come up with a "young earth" is to provide conclusions regarding Biblical content that are not, in and of themselves, in the Bible.
The whole "young earth" thesis is, in fact, extra-Biblical, as is "the Rapture", and the entire hierarchical structure of the various apostolic churches in Christianity.
How can these people live with themselves knowing that their entire body of belief (or their church structure) rests on manmade interpretations and doctrines?
Not that they should climb in bed with the Evos (who have, of course, their own ecclesiastical and theological problems), but just who came up with this "default position" deal?
The Bible does not say anything about the age of the Earth although it does suggest God was there at the beginning of time itself, and will be there at the end, and clearly states that this is a testable hypothesis should you have any doubts.
I know. I know. It's a waste of my time. But that doesn't mean that my mind still doesn't reel at the thought of supposedly rational people going out of their way to deny facts. It's something I generally associate with Liberals.