And it’s not always because, as is portrayed in the media, that they get rich from doing so.
I, or many other doctors, do not make a dime if I send a patient for an MRI.
Rather, it’s because there is financial incentive to see and churn through as many patients as humanly, or in some cases inhumanely, possible. Chris Rangel has a nice list, giving 10 reasons why doctors order so many tests. Part of it is placating the patient, another part is defensive medicine (“the common perception among docs is that it’s far easier to defend oneself in court using the solid facts of test results than to explain why a test was NOT ordered”), but those reasons, combined with the pressure to see lots of patients leads to this:
The physician intentionally places themselves in a situation where they are seeing a ton of patients a day and the best way to manage this is to order mega testing rather then to take the time to do a proper history and physical to determine if any testing is needed at all. Mega testing keeps the patients satisfied that something is being done. It keeps the lawyers away and it allows the physician to see far more patients per day then they realistically or safely or ethically should.
True, there are instances where doctors who own MRIs self-refer, and thus gives himself a financial stake in the tests he orders. But that’s a relative minority of cases.
Far more important are the financial incentives pressuring doctors to maximize quantity, which naturally leads to ordering lots of tests.