The thing about mental health is it is mainly for describing people who have serious trouble in society. You see this with homosexuality, which one hundred years ago was considered disordered because the nuclear family was not just a primary method of social organization, but also an economic one, so not naturally fitting into that pattern would make life difficult. It took changes in the economic and social patterns for people to look and say "Well, at this point we are making life difficult for them on purpose, if we let up they'll fit in as well as anybody." and bam, homosexuality drops off the DSM. 

Go forward 100 hundred years into a time where education is critical and your ability to do the work is integral to your future, and ideas like ADHD appear. One hundred years ago somebody who had trouble focusing in school could drop out in the eighth grade and still get a good job without too much effort. 200 years ago school wouldn't even be an expectation. But now, school is pretty damned important, and having trouble concentrating school can be considered disordered.

As the requirements for living a standard life become tighter, so do our definitions of disordered. 

Also why, though we all know politicians and successful businessmen tick off the boxes for antisocial disorders, we don't usually toss them into that category in a real way. Sure, they are psychopaths, but we as a society seem to accept psychopathy as necessary among the aristocracy. If it fits in with the model of social organization we've decided to go with, we just don't considered it disordered, even if those exact same traits would be considered disordered among the general population.