That's a bit of an overuse of the nostalgia filter, bud. Also, it's a judgmental generalization.
I'd say that, with a few exceptions, pop music in general sucks. It just so happens that stations that play classics find the good pop songs from previous time periods and play them, whereas stations that play modern pop have no quality filter because a lot of people who listen to them don't have a quality filter, either
Also, less-mainstream modern music is often really good.