I think it's a due to a combination of things. First MTBs went from flat bars to riser bars as front and then rear suspension appeared. Then the bars got wide

I think it's a due to a combination of things. First MTBs went from flat bars to riser bars as front and then rear suspension appeared. Then the bars got wider. I have memories of the bike magazines (Mountain Bike Action) declaring the bar end on a riser bar a style no-no. MTB takes style direction from motorcross and you don't see bar ends on motors. I've hooked my new 760mm bars on far more trees than my old narrow ones. While the idea of catching a bar end sounds frightening, think about what would happen without a bar end: the same thing. You'd hit the bars or your knuckles and get the same result. I do miss the extra hand position sometimes. I installed a pair of Togs (https://togs.com https://togs.com) to help with "thumbs resting over the bar".