Mountain biking has changed since the '90's when bar ends were common, even a bike from a few years a go will ride differently to a current bike, unless your racing now, most people will have a bike which is more of the All Mountain type than XC.
Riser bars are the main reason don't use them, they are still great on an XC bike w/560mm flat bar, but with risers going from 680-900mm wide, you get so much leverage from the bar, there is no need for any more at the end. Also, with wider and wider bars, having bar ends is a liability when going through tight singletrack; they also they just look wrong with riser which doesn't help them.