Maybe you just didn't realize it, because it isn't very common to see someone's full name? It was very much the norm until the 80s-90s, and even today I think the majority of women still go that route. I just spent a couple minutes searching Facebook to sanity check myself, and so far all of the women I'm friends with who are under 30 and married have done it.
I wouldn't use Facebook as a guide. My sisters all have done <First> <Maiden> <Last> for facebook, but none of them have legally changed their middle name. They just do it on facebook so that people can find them.
Most if not ~all of those women are doing it so people can find them on Facebook, and people in the States rarely use the middle name field anyways except for legal docs.
