According to an interview on the PopEater site:
Obviously, my wife has always been inspired by Marilyn Monroe...she bought her priceless piano and all that stuff. And I just like the idea that is was more than just naming our daughter Marilyn. I think that would've been a little too cliché. Monroe is a very strong name — it sounds really elegant.I guess it's "cliché" to name your child after the first name of someone you respect.
But this only spotlights the missed opportunity. Who wouldn't want a beautiful baby girl named Mortenson?