This was in my region report from this turn:
"Beziers: The population is growing 186 people through new births and immigrations. 267 people are leaving the region for the open lands nearby."
My region is less than half full. Yes, there are regions around with lower populations, but are peasants really going to go, "Hmm, I'm currently living in this region that's only 45% full, but I really want to go live in that region that's only 28% full. There's much more space there."