I don't think legality has much at all to do with why most pros aren't forthcoming about this stuff. It's because they are insecure and people will talk shit about them, which they will!
Genes are everything. But the biggest myth in all my over 30 years of following bodybuilding is that pros train like it's life and death. That their willpower and pain tolerance is on another level. A few do, but generally it's all BS. I know a pro who has been to the O stage several times and his training is pathetic. 135lbs bb rows, 280lbs deadlifts, 20lbs db curls and so on. Diet is shit too except for a few weeks before shows. And the female pros are even worse, top female pro bodybuilders. They don't really exert themselves, just go through the motions, laugh and gossip half the session.
Shitty bodybuilders are mostly shitty because of shitty genes. Not because they can't conjure that killer instinct. This is not to discount effort altogether. Some like Dorian showed what genes + training like a madman can do. High effort pays as long as the genes are there but most top pros don't do anything special as far as training.
When I was a kid I read articles about Arnold training to the point of passing out and vomiting. Some talked about shitting blood or even getting a fever after hard workouts. Then you see them actually "training" lol. It was all BS. Even Dorian's training wasn't all that when I saw his tape. Say one set of 6 with 400lbs on the incline with one forced rep. Yeah hardly something that will almost send you to the hospital with rhabdo.