My understanding is because votes are based on stake. It wouldn't matter how many accounts you have because your total stake, or voting power, would be the same.
You totally missed the point, I didn't imply it's not based on stake:
1) Why shouldn't I be allowed to vote for myself with my own stake?
2) What's preventing me from creating a delegate B) then voting for B) with A) which has the large % stake?!