Tj, there's something important that you seem to be ignoring. What is on the radio is not the only measure of what is popular in general. I actually agree that radio stations are not as good as they used to be, and seem to play a narrower range of music. But this is because, back in the day, the radio was the only real way to discover new music. Well, or live gigs I suppose, but those cost money as well as buying the albums. So the only way to really "try before you buy" was the radio, and so it covered everything because it needed to appeal to everyone including hardcore music fans.
That is not the case these days. Those of us who really want to discover new music do so via the internet mostly, and even within that there are a ton of different ways. So the radio is primarily for more casual listeners, those who don't take music too seriously and want something with a catchy hook, or a dancable beat.
But this doesn't mean that pop music is in any worse a state than it ever was. If you look at the album charts, there is a lot of really great, intelligent music in there.