Why are genetic mutations only among people from mainly Northern Africa, Europe, etc.?

Let's say I believed in evolution(I don't know if I do or not, and it's not because of religion(because I'm atheist)). Anyways, genetic mutations such as blue eyes and blonde hair that aren't beneficial for the surrounding environment are only prevalent in the places such as Europe. Why is this? Why not in Africa and East Asia? Was it just by chance? I'm missing something.