Older versions of US Core PractitionerRole profile defined "practitioner" and "organization" attributes to be 1..1 but this constraint was relaxed in latest version because it was realized that this is overly constrained for some use cases.

For example, it is not unusual for a provider directory to have information about a practitioner working at a location but may not have information around the associated organization / type-2 NPI.

It is also useful for some directory use cases to be able to represent a practitioner role at an organization/location without naming a specific practitioner.  For example, a generic role representing "physical therapist role at Acme Physical Therapy", in which case one wants to populate the "organization" attribute but leave the "practitioner" attribute undefined.

See https://jira.hl7.org/browse/FHIR-29680 for similar concern that was raised in DaVinci Plan Net IG which caused that group to avoid using US Core as base profile for exactly this reason.