It's all about money.
An insured client allows them to soak the insurance company for much more per visit than they could soak a cash paying customer.
It's economics at work.
But consider yourself lucky. The same doctor is more inclined to misdiagnose, prescribe unnecessary drugs etcetera just to boost their bottomline - at the expense of your health.
Like a car mechanic suggesting unneeded repairs a bad doctor whose policies are all about $$$, is best to RUN away from not walk.