I think generational drops still are part of the problem. We're churning out millions from public schools that can't even think, anymore, and that's what IQ really measures. Not accumulated facts.
Sure, importing the most dysfunctional cultures also lowers the average IQ, as well as limiting the number of smart people allowed to immigrate. Poor breeding like rabbits and the richer not breeding contributes to this.
We are becoming a dumber country.