Why do people consider it so bad to name one's children anything that can't be found in a baby name book?

I was thinking about naming my daughter Lily as a first name and Morelia as a middle name. I have received much criticism for this choice of name. I also find it aggravating that people accept misspellings of names as a way to make their "Shawn" unique from other people named "Sean". Why is this?!?!?!