I used to hike up a very steep hill into a park near our house in Colorado. On occasion, I would find myself hiking faster uphill than a mountain biker was riding uphill. A great feeling.
The problem is that that hill was right near my house, but there was no parking lot near it. So I was always fresh out of the house, and those bikers had ridden no telling how many miles before they even got to the bottom of the hill. And if they rode out of town, they had climbed a thousand or two thousand feet before they got to the place where I started. So it might be a nice feeling to pass somebody up, but the reality is you may just be passing somebody that could ride circles around you in any sort of even race. This plus the fact that very few people ride as fast as they can ALL the time.
Some people drive that way, too, maybe they think other cars just can't go any faster?