It certainly goes down to a mental or spiritual problem or whatever else it could be. Take for instance Bill Nye, he says he's willing to defend the evolution theory and never accept that the Earth is 6000 years old, even if it means going to hell. That guy has lost it, he's desperate and he's also desperately trying to hide it from himself, with the help of Satan of course.
The top reasons why people believe in evolution are:
It's promoted to young children as a scientific fact, through school, the streets, movies (like transformers) and they don't let them challenge it, they just dismiss the objections as being uncientific or as people not understanding evolution etc. Also when children think that most people or the people they look up to believe in evolution, they follow, it's a simple weakness of the human brain.
People who believe in evolution are easily accepted in the scientific community and they can get an easy job without losing it.
People who believe in evolution are not ridiculed in the majority of the scientific community, so they don't have to defend their position and more.
2 Peter 3:3 - "Knowing this first, that there shall come in the last days scoffers, walking after their own lusts.", some people want to believe they are the smartest, most advanced beings, or at least (since many evolutionists believe there is life in other places that are far advanced) want to be able to compete with other beings, and not be so overwhelmed by the power of the Almighty Creator.