Trolls are the least of many reasons people are drifting away from the bracket. But if people list several reasons and mention trolls, "trolls" is what people latch onto to discuss because it can so easily be dismissed by saying, "You can still have fun if you'd just ignore them! There, your problems with the bracket are solved." But quitting the bracket and telling the trolls, "BTW, go eff yourselves" is sort of like quitting a job you don't like to do something better and telling asshole co-workers what you REALLY think.
For all my friends who have quit twinking 19's (and yes, they have all quit twinking), it's been the "broken" feel of gameplay compared to what it used to be... the speed boosts, the taking away of leg armor, the general lack of class balance. You might say "no big deal" to these things, but that's just an opinion. In the opinion of some others, low stamina and lots of hunters = no fun, and no amount of saying, "Just use teamwork to work around it" is going to make them feel that it actually is fun. The things that initially attracted them to twinking are gone, and they don't WANT to adapt to something they simply don't enjoy. I don't think there's anything wrong with that.
And saying, "They're making excuses because they're no good and can't hack it" is just silly. How many 19's legends have quit? Were they all "bad"? Not everyone is interested in suffering through something they find tedious just so they can proclaim themselves badasses. A lot of people play for FUN, not as some crutch to their self-esteem. And I think you'll find that "fun" is a very subjective thing.