a.  They say that using a bike allows them to get much farther, in the same amount of time, than they can by walking. They also maintain constant pressure on land managers, to open more and more trails to bikes. Of course, all of these trails are already open to them, if they choose to walk. They also frequently claim that closing trails to bikes "excludes" them from the parks. This could only be true if they were unable to walk. Of course, they are able to walk. There's nothing inherently wrong with bicycling instead of walking; we all like to save energy, when it's appropriate. Use of a bicycle to replace automobile use is obviously beneficial. However, by the same token, replacing hiking with mountain biking is obviously not beneficial.

b.  They are interested in the quantity of nature they can see, rather than the quality of their experience. While riding a bike, especially over terrain as rough as a trail, one has to be constantly paying attention to not crashing. That makes it almost impossible to notice much else. (IMBA confirmed that in their "Rules of the Trail": "Control Your Bicycle: Inattention for even a moment could put yourself and others at risk,The rest of the lap dazzled us with stunning views of the azure waters below, although fast rocky descending and even more steep loose climbing meant you had to pay attention to the tricky trail.") By contrast, a hiker feels the ground, hears all the sounds and smells all the odors of nature and can stop instantly, if he/she finds something interesting. The brain thrives on stimulation. A biker has to travel several times as far as a hiker, to get the same stimulation as a hiker. (And, by the same token, motorcyclists have to travel several times as far as a bicyclist, and an auto user several times as far as a motorcyclist, since they are enclosed in a metal box.)

"Something I didn't know about mountain biking, at least on a trail this challenging: You cannot look up. Even for a second. To do so is to court ruin. Forget about the scenery, all that peripheral beauty gone by in a flash, the profound silence, the bliss of seclusion. Was that a bull elk up ahead or merely a juniper? Oh, how the rings of morning light smolder over that ridgeline ... Wake up! Dial it in, man! Head down! Eyes locked on the trail! Let your mind drift and you are toast."

c.  They are interested in thrills. Riding a bike on a trail, especially a trail containing many obstacles, or a trail one is not familiar with, is very challenging. (But if mountain biking is the high point of your week, as it seems to be for many mountain bikers, you must be leading a pretty dull life, off of the bike!) "The sensation of speed, the feeling of the wind whipping against your face as the ground turns to a blur beneath knobby tires is one of the reasons so many of us become addicted to mountain biking." 

d. It's an addiction. "Jake Legge, who will attend Moopark College in the fall, said the sport is addictive. “Ever since I was little we’d do vacation trips in Mammoth and we’d bike out there,” he said. “As time went on, we did more and more biking. Before you know it, we’re racing. We got hooked. Ever since, we just can’t get off the bike.”

It’s one of those kinds of sports ... it grows on you,” Corona said, adding: “It’s very addictive. If you like it, you’re going to like it a lot.”

e.  They are interested in building mountain biking skills and competing with other mountain bikers. The thrill of racing drives people to spend more money on their bike, and ride it harder and more often. Racing, up to and including the Olympics, drives a lot of mountain biking. Of course, it is also extremely harmful to the parks and natural areas that are used for practice! It is hard to think of any other (legal) use of public lands, other than hunting, that is as harmful as mountain biking.

f.  They want to get to their destination faster (not considering that the process of getting there is a major part of the enjoyment). Once, when much younger, I was hiking along a very boring trail. The thought came to me that if I had a bike, I could get past the boring section of the trail, and to the interesting part much faster. But about 2 seconds later I realized that if I could do that, so could everyone else, and the place would be full of people and ruined. That was the end of my (2-second) mountain biking career.

g.  "We mountain bike because of the euphoric adrenaline rush, but that adrenaline rush is made all the sweeter by the pain endured on every single ride." Greg Heil

h.  Example: "What do you enjoy most about mountain biking?" "Just the experience of being out in a forest on a trail, just flowing down it and enjoying the scenery. I know it sounds cheesy, but you really become one with nature. At the same time, there's the adrenaline rush you get from downhills and runner's high from climbing. It's a lot of stuff that's hard to put into words." Steve Ray, mountain biker