I wasn’t aware that famous chess players have a higher than normal incidence of mental illness. In the United States, purportedly, about half of the population technically qualifies for some kind of a mental illness . However the definition of mental illness includes a wide variety of behavioral issues such as alcoholism, p.m.s. (?), marijuana smoking etc. so that may inflate the number. They sometimes redefine the list identifying metal illnesses if some items become politically unpopular.
In my opinion the reason that the number is 49% is that if a majority were credited with having recognizable mental illness then there are various philosophical problems that arise such as the crazies are running the asylum kind of thing. Nations with a lot of psychiatrists and psychologists have much higher numbers of people with mental illness. Europe has a lot of psychiatrists and chess players so it may logically follow that statistics might show that a higher percentage of the population including chess players have mental illness. Fortunately, famous chess players often can earn good enough money to deal with their handicaps and illness challenges for-themselves instead of relying on social welfare benefits.
It is possible that having a mind running toward blindfolded, cool chess calculations detaches great chess players from the usual chit chat about Donald Trump. Democrats at least may consider that sic.
Being a great chess player may require a fanatical devotion to the game, and the game is rather worthless in any social application concerning survival. I recall reading of one great German chess player who starved to death at home during one of the wars- the first I believe, in a gentlemanly way instead of asking someone for help (maybe he couldn’t have got any help if he had asked). He was a famous chess player with a good chess game and bad farmer/soldier/forager survival skills.