When this happens, there's usually one or two things going on.
First, this time of year the sizable bass can be very nocturnal. You may have been hitting them right on the head with your flies and they just weren't active, or you were hitting cover that they would be using after dark and just weren't there yet.
Second, and more common, when every inch of the shore looks like it should hold fish because of the cover you're seeing, it's time to actually ignore the cover. What's that saying...90% of the fish are in 10% of the water? If everything looks great, then there's still going to be a lot of water that looks like it should hold fish but actually doesn't. That's when you forget about the cover and start looking at changes in depth and bottom contour. The biggest concentrations of fish will be at great cover that accompanies these changes.
One more thought...if the water levels have been dropping in the river, that can put the fish off for a while too. I'm not sure what the prevailing conditions were in that vein, but it's another potential candidate. I experienced it a short while ago on a usually reliable area of the CT River.
Whatever the reasons, it sounds like a nice stretch of river. Hope you get out there again with better results.