It's not so much that they prefer Biden over Trump. But they dislike Trump. I know people who cannot stand his antics on Twitter or the way he disrespects women or his blatant infidelity to his wives. However they strongly believe in conservative and Christian values and will hold their nose while the vote for him to try to ensure the supreme court votes their way on issues such as abortion. Trump knows this and uses it as a carrot to encourage these people to vote for him.