Insurance-based medical systems mean the patient has transferred responsibility for saying no to those actually paying the bills. They have to draw the line somewhere.

The United States Preventative Services Task Force[1] reviews studies and meta-studies to make recommendations about screening procedures. Their ratings are used by Medicare and Medicaid to decide what's covered and for which patients. In turn, many private insurance companies cover the same procedures. The USPSTF explicitly doesn't consider cost in their recommendations. Most often, they look at whether a screening reduces mortality rates.

1: https://www.uspreventiveservicestaskforce.org/

But you're not having cancer checked out, you're having a "spot" or a "nodule" or something checked out.

And the person that's making the recommendation on whether or not to check it out may get sued for $10M if they tell you it's probably nothing and they're wrong, but have no harm come to them if they tell you it's worth having some other doctor do a biopsy.

And they might make an extra couple hundred bucks every time you have to come back and see them to follow up on this spot.

And the radiologist interpreting the MRIs... the same perverse incentives regarding how they interpret a "spot."