Have you never been on a team? All members don’t think alike but they pull for the betterment of all of them! Politics is no different. You are called to work with those you disagree with. As sensible adults, you don’t take your ball and go home.
Trump isn’t being called to play on a team - he’s PICKING the team. Why should he pick someone who hasn’t supported him 100% compared to, say, someone who HAS?