I recently got my Technician's License and most of the rest of the class were first responders, including a fair contingent from the local 911 operation. I suspect that pattern could account for a drop in general traffic: those who are qualifying and training up as part of some future emergency response don't go out and chit chat much about dipoles and ducks, as enthusiasts are prone to do. They may not even join up with the ARRL sponsored disaster (emcom) response groups, but they are prepared through their protocols to transition over to Ham when the other forms of communication go down.

Not a commentary on RACES or ARES at all, they do great work. And sampling from a single technician's class is hardly scientific, but it goes along with a fairly logical course of preparing responders for when things go bad.