I am not aware of any effort to regulate or train bike mechanics. Sure, there are schools and there are chains that have standardization training, but there has never been an expectation that specific education is necessary to work on bikes any more than we expect the kid at Subway to have attended culinary school.
I learned to work on bikes by reading a book. Then I read the specific instructions for components I was working on, if available. Up until recently, this should have been sufficient to make a reasonably mechanical person be able to assemble and adjust something as basic as a bicycle.
The problem now is that all sorts of stuff doesn't work as advertised from the factory and requires techniques that aren't in manuals to be serviced. So the best mechanics are no longer mechanically competent people that can read, but witch doctors with prolific memories.
For bikes mid level and above, I would say the effective quality is much lower today than it was 20-30 years ago. The need for things like disc brake mount facing tools should alarm bike consumers - why are frames leaving the factory like that? Why does a DA hydro lever not work right if you clamp it too tightly to the handlebar? Why do Shimano shifters still eat cables after all this time.
Mechanics are dealing with a lot of junk, and the public might be reasonably upset that new bikes are much harder to get right than old bikes.