Doctors can charge high prices because they have low supply and high demand for their services.
No one is stopping a doctor from offering their services at $25 or even $50 per 30 min consultations. If doctor A was offering their services for X + e to insurance just to get X, and doctor B was offering their service for Y, and Y is less than X, then insurance would still go with doctor B even though there was no “e”.
Insurance companies solve the issue of a buyer having no knowledge about what they are buying since they also employ doctors to check others’ work, and to negotiate pricing as a group. Some countries don’t need this since the buyer is the government, but the government is still performing the same functions of negotiating prices and verifying doctors’ work.