I have a different perspective on this. I've always been interested in reading about the science of left handedness, because I am one. It's interesting to see how my brain is literally wired differently than others. How motivation and language processing are in different hemispheres of my brain compared to righties. But I never thought something was "wrong" with me, I just thought it was interesting.
Those who actually have diagnosed afflictions like autism and ADHD may also be interested in their brain wiring.
I think the trend comes from completely normal people who want to find an excuse to be a victim, which means they can defer responsibility of their lives to their "mental disorders," which of course has the effect of making highly insufferable people.