Cycling is a really good example because it is so stark: 1) If you win you make more money, probably a lot more money. I don't know the current numbers, but during the Armstrong years there were plenty of Tour de France level riders that worked wrenching bikes to make ends meet and lived with their parents in the off season. You had Lance on private jets, and then guys on the team making under $30k supporting him. 2) Genetics is huge, you can do everything possible and simply not be good enough, if you've dedicated a big chunk of your life to this dream, you've won at every level, you live a completely monastic lifestyle and constantly diet and you reach your limit the desire to get just a little bit better is strong. The drugs work. 3) If enough people believe that "everyone is doing it" then the psychology of cheating disappears. 4) There is no external pressure or risk; the teams and sponsors don't get burned. When Lance won on a Trek they went from being something like a $200m company to a $2.5B company. They may very well have played a part in it, perhaps unbeknownst to them, but they never had any jeopardy.
They're talking about what is physiologically possible after this year's Tour, it was a complete ass kicking. If your competition is doing things that are believed impossible, do you hang it up? accept defeat? Or rationalize that a few watts isn't really cheating since he's doing something impossible?