The article starts by saying no one uses them anymore and finishes by saying a lot of people still do. That aside, a couple of the posts above sum it up nicely, wider bars these days provide the extra leverage for uphills and also make reaching the bar ends harder. The fact most people just want to go down hill makes them also redundant for those users.
I still run bar ends on a lot of my bikes due to the narrow bars to aid in climbing. It is nice to have extra hand positions too for longer rides, though that is purely for comfort and not performance. As for catching them on things, only ever done it a couple of times over the years, and that is on trails that are very narrow, ones that you could not ride down on modern bikes as the bars would be too wide.