Yes, CHR is trending down nationally. Shawn Ross complains about current product pretty much every time he writes about CHR.
This may be a separate topic, but I agree with Sean. When you're a currents-based format, and the new music isn't as dynamic, the audience drifts away. It's a music problem that becomes a radio problem.
Meanwhile, other formats might be creating more exciting new music, and marketing it better. That leads to increased ratings for those other stations.