You raise a very interesting topic for discussion, Bill.
There are certainly several perspectives to consider. I can certainly understand the financial implications and your not wanting to purchase medications, perhaps at a higher price, that you already have.

Patient safety is the sole reason that hospitals have protocols regarding medications during hospital stay. Here are some of the reasons why.
The use of a patient’s own medication(s) is discouraged for safety reasons, namely because the storage and handling prior to the hospitalization is unknown. But a patient’s own medication may be used if the patient has written order of the physician or other authorized prescriber. For each medication, the order should specify the medication, dose, frequency, indication, and route. All medication that has been brought in is given to a pharmacist for identification. If the medication cannot be identified, the medication may not be administered.

Thanks for raising awareness about how Medicare parts B and D cover (or don't cover) prescription drugs while in hospital for outpatient settings like an emergency department, observation unit, surgery
center, or pain clinic. It is well explained in this document.
- How Medicare Covers Self-Administered Drugs Given in Hospital Outpatient Settings: https://www.medicare.gov/Pubs/pdf/11333-Outpatient-Self-Administered-Drugs.pdf

Bill, it sounds like you may not have had pre-warning of your hospital admission and therefore were unable to obtain written order from your prescribing doctor. I'm glad that Mayo Clinic was able to accommodate you and that they will administer the medications you brought in.