(Yes the Conspiracy, the Dunning Kruger ref.)
While I agree with some of what you say Oliver, and accept the last point re the tldr [See edit on op], which I suppose was meant to provoke a response, or an explanation of why they have not trained in order to improve riding if that's so important to them.
There will be people who who refuse because of pride, and it's that pride, in their average cycling skills, which prevents them from accepting that they are average skills.
I also think that to some extent many people assess their skills in bike handling as good which is probably true for many on-here. People may be used to being cut up in traffic, or squeezed drivers passing close, or annoyed at pedestrians stepping out in front of them and think that's unavoidable and normal because of "the idiots out there", rather than thinking what could they have done differently.
As you know from undergoing training and perhaps reading Franklin etc. is that much of the training is counter intuitive and counter-car [driver] is king culture, which makes it more likely for people not to know (or care) about what they don't know.
And of course, George Kelly, (who brings Plato to Constructivist Psychology where he describes a person as a scientist experimenting with their constructs , some open to change some less so)), says, everyone construes the world differently based on "their knowledge-states and pre-existing beliefs, as well as the degree of openness that they have". So my generalisation my be unfair to some but not for many others.