I think the first part is because society degenerated in the social/psychological department, given the circumstances. The second part is about shekels, goyim dont breed and goyim go round. Bigger minority population means better psychological steering of the goyim. Cheaper labour force means more shekels in short/mid terms since you have more consumers, some will work and the rest will get fed by the gross of the population. So for the higher ups it is a win/win situation in a certain timeframe.