Insurers aren't more generous - they have negotiated rates. They're never paying 100% of what's charged. Some providers are better at negotiating, or have more leverage, than others.
https://www.quora.com/Why-don-t-psychiatrists-do-talk-therap...
You've shared a belief that a patient will continue to see a psychiatrist when not being given drugs. Since psychiatrists don't tend to do talk therapy, I will reiterate I don't believe this is correct.
I'm sure there are exceptions- a wealthy person might find a Doctor Frasier Crane type Doctor to do talk therapy- but they would be paying out of pocket. I know the local Ivy League school only takes a special Ivy League insurance offered only to the Ivy league school's students and staff. The wealthy- and their Doctors- don't need to worry about the "rules" set by insurance companies.
Someone who has been through med school would not typically lower themself to that rate, nor do I buy the idea that some insurers are inexplicably more generous and pay doctor rates for non doctor work.
Remember, talk therapy does not require as much education, you do not need a phd or md to do it. An MD would not get doctor level payouts doing talk therapy.