Originally Posted by
devianb
For me the corners of bullhorns offers the best hand position for the longest period of time.
I'm of the same mind. Switched my drop bar to bullhorns for $10 in parts from a swap meet.
To answer the OP a single hand position pressures the same spots on the hand leading to numbness and fatigue. Drops have 4 different hand positions, thus easier to give different areas of the hand a rest.
Having said that opinions differ which is better for long distance riding. Some like flats and some like drops. Keep in mind not everyone likes laying out to ride so drops and aero bars are of limited use to them
IMO the problem with trekking and aero bars is added weight. Trekking bars can be wider making it more difficult to carry the bike up stairs or into hotel rooms. Aero bars take up valuable front end space limiting handle bar accessories or a gear bag options. Can't say I've ever seen a bike tourer with aero bars, but I'm sure there are some.