Why? You do realize we still don't have marriage equality, right? So far we've got racial and gender both covered. But that's not all cases. We still have polygamy and 'multiple consenting individuals' to go. AFAIK I'm still unable to marry my AGI lover.
There's also the issue of married couples gaining legal benefits that unmarried couples don't get. That ain't equal. From what I can tell, the end game is to just abolish marriage/unions in their entirety and give people equal rights regardless.