Why must the Prime Minister be local?

Does being born in one country automatically make that someone,
More virtuous, more loyal to the country, less likely to concentrate wealth unto himself, a better leader and other arguments for only having local people for the job. Sadly the answer is no. If you look a at the most African nations there are as worse off and have as much wealth plundered pre-independence and post-independence. The colour of the skin and or land of birth is not as important as the character. Better to have the best person for the job than anyone less just because he is my brother.
Carlos Ghosn turned Nissan around and not some Japanese man. Now I don't think anyone in Nissan if given the chance to do it again will choose anyone other than Carlos just because he isn't Japanese though this was an argument used as reason for not agreeing to his appointment.
The day I know Africa will turn for the better i the day they hire someone who is good at his job to be Prime Minister whether white , yellow or red or even stripped instead of just choosing some warlord because he is local.