Not sure whether it matters now whether he is being 100% truthful or still trying to construct a narrative to protect past doping he got away with. But you can clearly see why doping is such a problem in athletics just based on the background that Robertson talks about. Survival in the sport is directly based on sponsorship dollars. Sponsors put way too much pressure on athletes to perform at a top level indefinitely. Then, you have to go out and compete against competitors who are probably doping. Add in a few bad injuries and an aging athlete and it is easy to see how overwhelming the pressure would be to dope just to stay in the sport.
If the sport really wants to stop doping (not sure it does), then it has to move past just sanctioning athletes. Sponsors should be required to pay a living wage for the term of the contract with athletes without regard to performance. If sponsors want the benefit of having their gear on a national champion, Olympic athlete, etc., they need to bear the burden of staying with athletes through thick and thin, Sponsors cannot just skim the cream off the top but need to be required to support all athletes to make sure that they do not fall under the pressure to dope due to threats of getting cut off.