Originally Posted by
jmblur
Mountain biking is very different than road/touring biking. The "attack position" puts you far further forward on the bike with your upper body with almost no weight on your hands, in a position to drive down on the hands to pump terrain or pull back and up to unweight the front. Its much more like doing push ups and deadlifts than it is sitting for hours and hours. Not that there aren't situations where you're chilling there for an hour long climb, but the bars are designed for aggressive riding. More modern bars are also much wider and more swept to enhance control while leaning the bike way over (rather than leaning with the bike), which a flat hand position allows much easier than a "neutral" hand position.
Tl;dr: mountain biking bars are designed for dynamic motion, not static comfort.
+1, That is a good explanation of the difference. That is what ergonomic bar ends are for. You get a versatile setup which will give you different hand positions depending on what type of riding your doing. My commute consists of some off road and some paved road so I use both positions. I agree the vertical wrist is more natural for road riding and use the vertical bar end for that but switch it up often to stay comfortable. Its just like going back and forth from the top to the hoods on drop bars.