The single biggest factor is the cost of medical education. Once a person spends a fortune getting their degree, it creates a gated community that works to preserve its privileges, deny entry to other cheaper alternatives, and keep prices high across the eco-system.
You will see this in any field that transacts with high value goods: real-estate, enterprise software, weapons of war, investment bankers handling M&A ... the higher the cost of the product, the more the people dealing in it feel entitled to charge for their services.
You will see this in any field that transacts with high value goods: real-estate, enterprise software, weapons of war, investment bankers handling M&A ... the higher the cost of the product, the more the people dealing in it feel entitled to charge for their services.