I will let CMS answer that
"Q: Why didn’t CMS include all health care settings?
A: CMS is using the authority established by Congress under the Social Security Act to regulate
Medicare and Medicaid-certified health facilities. Sections 1102 and 1871 of the Social Security
Act (the Act) grant the Secretary of Health and Human Services general authority to make and
publish such rules and regulations, not inconsistent with the Act, as may be necessary to the
efficient administration of the functions with which the Secretary is charged. Citations to the
relevant statutory authorities for each specific type of provider and supplier are set out in the
discussion of each provider- and supplier-specific provision of the regulation. This authority
does not extend to certain facilities nor independent physicians/clinicians. "
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