Because overpopulation is a myth, the problem is obviously overconsumption with the US annually wasting 4 times africas annual import in food.
We don't have enough cows in the food supply to allow everyone on earth to eat as much beef as Westerners do. The same applies to fish. Same with fossil energy.
etc.
As living standards rise around the globe a greater proportion of non-westerners are getting access to the trappings of a Western lifestyle including the disproportionate ecological footprint.
We do not have the capacity to produce enough, for long enough to satisfy those needs and that will eventually lead to supply constraints and ecological imbalances.
Tens of millions of people are lifted out of poverty each year, and through the power of international trade, they are just as entitled to access global resources as we are.