"Dumbing down" is not a new concept. It's been going on for years, and when popular culture is firmly fixated on what passes for entertainment, is it any wonder that "general knowledge" is the first casualty? Conversation is also a dying art, and the current standard of both spoken and written English is appalling , even from "Auntie BBC" on occasion.
At the risk of sounding elitist, I would also note that those of higher intellect who make up the professional classes are either breeding later or even not at all these days, whilst those who are perhaps less gifted in that department are still producing children, as ever. So the gene pool is weighted in their favour, with inevitable results for society at large. A depressing prospect, and I can't see it changing for the better in my time...