Why do some republicans?

Why do some republicans still believe that gay marriage should be banned and don't believe in evolution? Why are some of these republicans still stuck in the 1900s? A lot of them say gay marriage will destroy the American family, so I guess a 50% divorce rate isn't doing that and a lot of them say that a child needs a mother and a father to be raised properly but then they praise single parents? How do you have a mother and a father if you were raised by a single parent? Seriously why don't Republicans give up on their ridiculous views?