That's nothing more than cultural bias.
Plus there's always context. This wasn't just some teenager worried about not being asked to the prom. This was a kid that was facing having is entire life destroyed apart by the government.
That kind of situation is quite often NOT portrayed as a sign of mental illness when the result is suicide. (even in the West)
The plea deal offered by the government was six months in jail and a felony conviction. Yes, the punishment is out of all proportion to the crime. It's wrong. It's a bullshit deal. It's six months more than anyone on Wall Street served after they blew up the banking system and destroyed the world's economy. But most people, faced with the choice of being unjustly convicted and losing six months of your life, and losing the entire rest of your life, will take six months. It wasn't the end of everything. After six months for trying to liberate the entire contents of JSTOR, he would have come out of prison a martyr and a hero. Serving time for an idealistic, altruistic act like that would have given him a credibility that no other activist had. He would have had the rest of his life to use his notoriety to push for internet freedom.
But that's the kind of optimistic, lemons-into-lemonade kind of thinking you just can't manage when you're severely depressed.