Why does USAA extend membership through legal same-sex marriages?

I have used USAA for my banking since I was 18 and have loved it, Most of my accounts are there now but that might be changing as my partner of 5 years is getting tired of not being a member and of being referred to as my "roommate" by people at USAA when he has to call in about something. We are getting married this January and I called USAA to see about making him a member as the spouse of any other USAA member could be but was told that USAA does not extend membership to spouses of same sex marriage.

I will miss USAA but it is not worth how it makes my partner feel every time I have to call in about something for him since they won't talk to him about stuff since he isn't a member.