As I mentioned in my comment, sociopolitical values clearly play a role, but I'm not so sure people are leaving the church primarily for overtly political reasons. I think even if churches stopped being involved in politics, young people, especially young women, would still find that their own sociopolitical values clashed intractably with the values of sexist/homophobic churches.

Why would a young woman want to be part of a church that barred her from leadership positions, when she's been raised to believe that women are equal to men?

Even if her church stayed out of politics, she's very likely to find that unacceptable and to drop out of organized religion rather than to participate in organized sexism.