It's a good question, and I don't know. I would like to think that cheaper hiker biker sites should encourage more to cycle tour. I suspect it's just not a priority to even set up areas, let alone make it easier to research for them.
I'll ask at velo Quebec sometime about this.
The thing is, for many of us accommodation is lower on the list of our concerns. We'll stay
wherever for the night. Much higher on the list are things like ... are there interesting things to see along the way and how are the roads for cycling.
So while a hiker/biker site might be kind of a neat feature at a campground, it's not going to be a make-or-break factor in choosing a route.