No, it wasn't because he was discovered. It was because he was being harassed by folks and media. To make it worse, people harassed his employers so much that they distanced themselves from him. I'm not surprised somebody wasn't able handle an Internet and media mob.
When your whole sense of identity (in this case running marathons) is ripped away from you (whether or not you cheated) you no longer have a reason to live. Unless you have other things to live for family, work, whatever. Other senses of identity and self.
I think, generally, the abuse that's occurring here is that people willfully raised the profile of a perceived wrong. Lobbying the people who run the races or local papers that ran stories about him to correct those things is appropriate. The national media showing up and people trying to bully or harass him crosses over into ethically bankrupt behavior under the guise of "justice".
I'm not clear on the suicide. Usually when men commit suicide, it is not survivable. I don't see how jumping into an an empty LA river channel would be considered "unsurvivable." Standing at the brink, I'd expect someone like him to realize, "this is no good... I might survive." Isn't it possible he was pushed? He did have future plans to deliver lunch to his wife.
The bridge is maybe 18 feet above ground level and the river bed is maybe 35 feet below ground; about 53 feet of total fall, on to concrete. That's a very big fall, and his advanced age makes it even more dangerous.
I don't think the theory that male suicides are rationally evaluating success probability is especially sound. But even under that theory, it's a hard fall.