Harold Mass of The Week acknowledges that the GOP is firmly pro-marriage and Brady's ouster is a sign of that fact:

In a widely expected move, embattled Illinois GOP Chairman Pat Brady resigned on Tuesday. Brady said he wanted to spend more time with his family as his wife fights cancer, but social conservatives have been calling for Brady's head for months. They're angry over his support for a gay marriage bill floated in the state legislature this year — the latest in a series of similar measures taken up across the country.

...No matter how Brady's departure is spun, the takeaway is that the Illinois GOP is doubling down on its opposition to gay marriage. Though "it's pretty clear that support for marriage equality is what forced [Brady] out of office," says Doug Mataconis at Outside the Beltway. After he came out for the marriage bill, 50 conservatives called for his resignation at a meeting in April.