It's one of the many current 'crazes' that people are going through. Instead of looking at real issues like, "These guys were golden gods with millions. Now nobody cares, they have a lot of free time on their hands, don't necessarily have skills or even an idea of how to function in normal society, and generally watch their wealth diminish (even if they're not poor, they're probably not filling the coffers unless they invested very, very well)", we invent a craze like "BRAIN DAMAGE".
That's not to say that ramming your head into something over and over is a good thing, but I think the problems many former players have are much more nuanced than their brains being damaged.