I'm actually surprised by the bolded comment, coming from someone of your intellect (or perceived intellect that is).
The opposite of your statement is easily proved true along similar lines of the theory of Pavlov's dog. People, in general, are not being conditioned to serious music or anything serious in general would be a much more accurate statement. IMHO, the dumbing down effect is the conditioning the people have been given, and this dictates what is perceived to be what people want. Today's generation is raised by the TV, the Radio, and the Internet, not by their parents and not by history. The peak conscious era of Hip Hop culture was well saturated and well received by the likes of various ethnic existences, in large part due to the saturation of it. The kids of today have the music on the radio of today in their heads because that is what they are conditioned to and what is readily available in free dose form.
It's not really about conditions, it's about the function that music plays in people's lives. It is very few people who listen to music because of the music. The main function of music for the majority of people is as a tool in the quest for ensuring reproductive success. This is nothing new, it has always been the case, since tribal prehistoric times. Even classical music, which today is a very high-brow thing, played that role at the time it was created - the aristocrats were having balls where they would dance to it, and the main objective was to hook up with an attractive member of the opposite sex. The composers and musicians were probably interacting with the music at a higher level, and there might have been a few true connoisseurs, but they were certainly in the minority.
The problem is that this has worsened in recent times. If you look, for example, back at the hippie times of the 1960s and 1970s, it was common for the people who listened to the music to also sing and play the guitar (owning one was really common). This does help elevate one's appreciation of the music as your are not just a passive listener. Old school hip-hop was very similar - block parties, break dancing, etc. And those were much more relaxed times when people first, did not have to worry so much about their immediate future, and second, did not have a zillion things competing for their attention at any given moment.
What we have today is quite different - we have entertainment that is consumed, and quickly discarded, with very little engagement on the part of the people listening to it, and we also have listeners with extremely short attention spans and very limited understanding of the world around them (a paradoxical consequence of the internet age, which one would have expected to make people a lot more informed given how much information is readily available, but has in fact done the opposite due to the inability of most people to integrate information, the large amount of misinformation on the web, and the fact that useful information has to be actively sought, which is rarely the case). Non-mainstream music is also readily available, and for a minority of people this is a blessing, as they can easily find what they are looking for. But it's a minority.
Find a random sample of people around the age of 30, and ask them what they were listening to 10 or 15 years ago. I can answer that question going back to when I was 5, you and most people posting here can probably do that too, but most will be unable to remember anything. Because what they listened to never left any lasting imprint on them, which in turn is due to the fact that they never listened to it for any other reason than that it was what the females in the clubs they were going to at the time liked.