Its not as rational as all that you know! We have a culture where salary can easily be completely unrelated to your ability or worth - we recruit management grades disproportionately from only a few universities without accepting that they do not recruit on ability, but on income alone.
We have nothing like an 'IQ' rate where intelligence is guaranteed to be rewarded, or similar for capability. One can meet dazzingly brilliant people earning bugger all and the dullest of the dull incapables earning huge salaries.
There is no universal requirement for continuing professional development, the addressing of skill fade, or even ability requirements for different level jobs.
It is still more likely for example, that you can move from a company where well-motivated intelligent creative staff are paid £10k a year or less (internships alert!) to one where dull plodders with poor management skills and a will to screw customers are running failing, con-based businesses over and over again without utilising the potential or inherent qualities of their staff.
I have met recently people with similar background to me, similar knowledge, fewer language skills, participating less in professional development programmes and who are amazed that I know so much about an area I don't work in directly who are in senior positions, earning large amounts where I am not. I have also had experience of the other side, meeting people who are far more talented than me, better at handling people and highly creative and knowledgable who are earning very low wages on a dead end career path.
People are sadly not paid what they are worth, but some function of who works around them, what their expectations are, a localised view of the worth of knowledge, social factors like do I like them, do I fancy them, do they talk like me, and also the available money in that company and its motivational philosophy.
Sadly the poor consistency across the country means that we probably have as many untalented well-motivated and well-rewarded people as we have damaged, low self-esteem poorly rewarded people with exceptional talent.
The shame of our nation is that the management layer that needs to solve this problem are often the dullards who went to private school because their parents had money, not because of ability, went into a top university because of the application bias from private schools, not because of ability, got an accelerated overpaid graduate position because the employer thought that if they were recruiiting from 'top' universities they were getting the most able, proved to be ineffective, but weren't noticed as being such because the only other people for comparison were people who had been through the same biased recruiting programme.