That is an outstanding observation!
There are several things generally available to public out there about marketing the services of magicians. There are reading materials and other recorded materials you can buy. The best convention for the business of magic only covers children's magic. That is KIDAbra held each August in Tennessee.
Reality is that commercial magic as a business is like any other business. The best sources of expert marketing are private sources that most likely are employed by well-managed businesses willing to pay handsomely for their services, loyalty and exclusivity. It makes it hard for someone trying to get in. It's simply another league.
There is a saying: Whenever you see a turtle on a high stump, it is reasonable to assume he did not get there by himself.
Marketing is the secret to many entertainers success.
In my nearly fifty years in the professional entertainment business, I cant honestly say that I have ever met a self-marketed entertainer that enjoyed the success of a professionally marketed entertainer. There is a very great difference. However, I have met hundreds of self-marketed entertainers who have enjoyed a very good and productive life. Many are found on the Internet and have good advice to offer.
In universities it comes as a shock to lay people to learn that the best earners on the faculty of the business school are typically in the Marketing department. They have more options to earn money than most of the rest of the business faculty. (They also leave! Other times their availability to the university is actually due to the sponsoring efforts of private industry. I can only remember two who were not.)
Your observation is more telling than we like to admit.
Good luck on your voyage.
Magic By Sander