Nobody does. The real translation is old people don’t want to change doctors.
The refrain of "people like their health insurance" deliberately conflates the two. People like their doctors, not their insurance. Doctors accept multiple insurance companies.
Some do, but not all. One of my providers takes exactly one insurer, which I do not have, so pay out-of-pocket.
Luckily most insurance companies allow you to submit receipts to receive credit towards your deductible.