I definitely am surprised at this. I don't know many conservatives willing to be permanently tied to a liberal. Especially when, more often than not, "liberal" relationship behaviors are inherently more chaotic by definition.
I also couldn't imagine being married to someone with whom marital relations would stop because of partisan politics in the media.
Don't be surprised. This is about dating, not marriage. When it comes time to tie the knot conservatives (usually) stick with other conservatives.
Maybe the conservative guys realize that they won't be permanently tied to a liberal-- over time, her political views are quite likely to shift into greater alignment with his. I know that mine certainly have.