Northern dialect government officials in Saigon?

I’ve lived in Saigon for a bit now and I noticed whenever I land at Tan Son Nhat all of the immigration officers speak Mien Bac (or northern dialect) and I’m used to mien Nam (southern dialect). Its very difficult to understand the northern accent (similar to how US folks can’t under stand southern US accent for an example) Even running into government people in central Saigon I’ve also noticed this as well. Why does Hanoi employ northern folks in a Southern region? Why don’t they just hire the Southern labor force? Surely it’s much more expensive to relocate a family in the north to the south and than to just pick and develop someone from South. I also noticed this trend in the Vietnam national football team, all the players are from the north and none from the South. I’m sure there’s hidden football talent in the South that just needs development