My dentist is an old school dentist who is a total master artisan when it comes to dental work. He just about cured a TMJ problem my wife had and has done masterful work on my lousy teeth. He made good money, but never got rich off of dentistry. Now, there are dentists popping up in my neighborhood who do tons of cosmetic procedures that are all cash procedures with no insurance pricing. Their profit margins on these procedures are huge and a lot of the work can be done with assistants and hygenists. So, they can crank out a bunch of procedures at one time. Then, they come up with a name like "Glynt Dentyst" and set up a franchise all over making money off other younger dentists who have no book of business. The money gets pretty big then.
$30k for a running coach is ridiculous for an amateur runner, but people with big money spend that much and more on a lot more idiotic things. Country club memberships, hunting leases, bespoke clothing, private dining clubs, high end bourbon and Bordeaux futures can be $30k+ a year. At least with running, it is something that gets you outside and out in the public with the rabble instead of being sectioned off with the ultra rich.