> has to meet regulatory standards

Genuinely curious, what standards exactly, for a stethoscope?

A commercially sold hospital stethoscope is a legally marketed medical device made under a manufacturer quality system, with labeling/instructions, device listing/registration obligations, adverse-event/complaint processes, cleanability expectations, liability, warranty, consistent materials, and repeatable acoustic performance.

An open-source 3D-printed stethoscope is a cool project, but unless it is produced and controlled as a medical device, it is not equivalent to what hospitals are buying for daily patient care.

Personally, if I was a hospital or a doctor, it would be a no-brainer for me to go with the commercially sold stethoscopes. All those factors I listed above, if neglected, can end up costing a lot more in terms of consequences. I would rather pay a fixed extra overhead price per unit to sleep well, knowing I don't have to worry or think about those factors at all. And, I would assume, most of the patients would be in favor of that as well.

In the UK it would be Class Im - so low risk device that sits outside the body, with a measuring functionality.