Because it's true, and he tried when he wasn't being prosecuted. The point has that some people are unfortunately prone to chronic suicidal episodes. It doesn't make sense to blame some external factor in cases like these.

If he was cut off in traffic and then went home and committed suicide, would you say that the driver that cut him off was responsible for his suicide. You might say that's because no normal person would commit suicide over that act, but no normal person would commit suicide when offered a 6 month house arrest.

And if you were going to commit suicide because of a long prison sentence you would probably do it after you were found guilty, like the guy who drank poison right as he was found guilty of something that would put him in jail for most of the rest of his life