Drop bars allow the rider to make full use of their back, stomach, and leg muscles when going uphill. I can put a lot more of a push on the pedals when using drop bars. The tops of the brake levers also make a better place for my hands to rest than the handles with a straight bar.

Mountain bikes are seldom ridden for many hours, much less long sustained grades as is often the case with road bikes. With mountain bikes the trend has been to wider bars to provide more leverage with the much larger and heavier tires in use.

Drops make no difference in overall stability which is primarily a function of the head tube angle and the amount of fork rake.