it can’t be that hard to have an automated lock on the door.

No, but human factors dictate: it can be that hard to use the lock properly.

out them further away.

Some places do this, other places don’t have a good layout to make metal detectors a practical thing for the MRI suite.

with MRI machines costing what they do, these aren’t the prices you would worry about.

Often (depending on location), the most expensive part of the MRI suite isn’t the device, but the room itself.