To the grandparent post, you'll probably be interested in the recent documentary "Icarus". It's on Netflix.
Most amateur sports from what I've found such as cycling (bikes not gear), martial arts, football, you can bet most people are using to some degree.
The op mentioned masters class, and there's a tight correlation there to older men being prescribed trt. A lot of people also take that and then up the dose a bit more to the point where they're running a full cycle and should be taking an AI.
That's another aspect as well where people will claim it's just trt dose, but no I'm sorry but when you got puffy nipples because of your trt dose and no AI you're on a full cycle.
Also, it's probably somewhat of a "who cares anyway?" attitude. They're not gonna go pro, they're not getting tested, etc. Any kind of competition involves someone bending the rules, like it or not.
Age groupers are much more persistent, they have their hobby permanently dialed in, they wouldn't even know where else to search for a sense of achievement. They are used to getting faster from a combination of better technology and better training, and to some of them doping might seem almost like a natural extension of carbon and training plans when those are maxed out. Fortunately, the deep end of both the training and the carbon is so far out that I am confident that it's still only a small minority who falls for the temptation (the very few testing that has happened on the amateur level concentrated on the top results, if doping works, that's where you will find the dopers)
(source: getting more carbon and more training as I get older)
Triathlon bike rules are looser, but most triathlon courses have less climbing so aerodynamics take precedence over minimizing weight.
carbon -> carbon fibre bike parts, which is way lighter and way more expensive but makes you go faster with less effort
The race organiser does not pay for the testing directly. British Cycling takes a small levy for every rider taking part in a race and I imagine this goes towards paying for the random testing.
The UK anti-doping website has a list of all current and historical bans for drug test rule violations covering a wide range of sports:
https://www.ukad.org.uk/anti-doping-rule-violations/current-...
https://www.outsideonline.com/1908791/i-couldnt-be-more-posi...