Handlebar plugs are essential really. Much harder to jamb a bar through your leg if the bar is plugged...
As for why bar ends aren't popular on MTBs now, they aren't that much use in the bush, you can't change gears when using them. The kind of people who rode MTBs with bar ends used them on road, there are much more suited bikes like hybrids, gravel grinders etc etc now that do the same thing.