Why does everyone want to use a surname for a baby's first name?

It really gets on my nerves -- Some don't but a lot do. Like for example, my fiance's last name is Keaton and people are really making the boy name "Keaton" trendy now, no matter how they spell it. I've seen it spelled Keaton, Keeton, Keighton, etc. It gets on my friggin nerves? Why do people do this?