Apparently, according to a cyclist friend of dhs they use the roads because 'its a road bike, not a path bike'.
In Sussex, they spent hundreds of thousands on a lovely, level riverside cycle track, approx 5-6 miles long. It saves cyclists from having to ride on a narrow, winding, up-and-down NSL road, that carries heavy traffic including enormous HGVs that have just got off the cross channel ferry. (Dutch flower lorries, mostly, I seem to see one every time I use that road).
Do they bloody use it? No they don't. They still ride on this C-category road, which has only 2 short stretches where overtaking is possible. If there is oncoming traffic on these stretches, you can be stuck behind a cyclist for almost 7 miles. On the uphill stretches, this can be at not much more than walking pace. And sometimes at this time of year, you get big groups of cyclists so that make such a long line that you can't pass them all on the short stretches that are straight enough to overtake safely.
On occasions, I have counted queues of more than 20 vehicles stuck behind a cyclist. They never pull over to let cars past, unlike tractor drivers and horse riders.
One of the best things about changing my job is that I never have to drive down that road to see clients. I used to have to do it several times a week.