When I was about to get married, I was entering grad school with the intention of getting a Ph.D. My husband wanted me to keep my last name because he said, "It wasn't my family that worked so hard to help you go to school; your family is the one who deserves the credit for that." I had never even thought about it, really--I'm from a traditional family and just assumed I'd take his last name.
But I wound up keeping it, and while I'm sad that our marriage didn't last, if I remarried, I'd have to think long and hard about this.
I also have to admit that it really churns my butter when people like myself who have "non-traditional" opinions about married names are automatically branded as Godless, soul-less, heathen liberals who are all part of Satan's plans to tear apart the traditional family. It's fine to believe in traditions, but please don't tear apart everyone else without at least hearing their reason first.
For instance,
* I've known guys who grew up in unhappy families but felt accepted into the family of their future wife. A man in this situation might want to take her last name instead.
* I'm from a small family in which having an only child has occurred a few times. If I were from a family with only one child and/or all girls, I would definitely want to carry on my family's name in some way.
* Some people very closely associate their identity with their name. I've known adopted Asians like myself who wished to change the American name they were given back to their original Asian name because they identified more with their Asian heritage. I myself am the opposite. I feel very comfortable with my American name, but I understand that different things work for different people.
And because a sense of identity, belonging, and carrying on some kind of family heritage can be so important to some people (especially adoptees), many will want to keep part or all of their name for the rest of their lives, even if their marital situation changes.