The machines are expensive (millions range per MRI scanner), staffing the machines nearly around the clock with highly educated technologists, repair/maintenance of expensive specialized machinery, radiologists to read each scan (esp with a current shortage), means it’s very expensive to set up and run an imaging center. Opening and owning an imaging center used to be seen as fairly lucrative. and many radiology private practices did just that, however, the economics have changed over the years with dropping reimbursements, staffing shortages, etc and now often these imaging centers are seen as a liability rather than an asset.

Excluding the cost of X-ray/CT/MRI machines, operating them, getting people to them and through them, sometimes injecting contrast, and sometimes dealing with side effects of said contrast, radiologists, I think. You can scale all of the above except interpretation. AI is the natural next thought for how to scale that part, but it's been thought that this would happen any moment for over a decade.