There's surely a promotion problem, and there's surely been an economic problem: but the main problem is unfortunately probably more serious. In the overall scheme of things, motorcycling is a pretty small niche sport- and roadracing is a small niche within that.
I'm starting to feel that roadracing is just not engaging enough for many fans (for lack of a better word) these day- the mid age-range folks are losing interest and the young ones aren't getting any. As brutal and difficult as the racing is, without an appreciation of what the riders are actually doing it looks unexciting compared to, say, supercross. And that's in person. It's even worse from a TV perspective-- as roadracing doesn't work well with the "switch the camera/image every 2-4 seconds" viewing that today's seemingly ADD-afflicted young fans need.
I've been watching/enjoying this stuff since the late 60's. Been peaks and valleys for sure- but it "feels" more serious now.