> where there is only space for the top few % to succeed

Typically these careers have something else in common: individuals at the very top have practically unbounded wealth and a very visible public profile.

That fact is actually the cause of the fact that only the top few percent will have any income at all. In most careers supply and demand stay reasonably in balance as people filter themselves out due to lack of real interest or ability. But with these 'careers' there are enough impressionable young people who see the extreme successes and are tempted by them that the supply of prospective participants far outweighs demand. This leaves the vast majority of hopefuls without any prospects whatsoever.