We know, and there have been attempts to return it back to person_id. @daniellameeker (or @Daniella_Meeker) initially wanted to keep it open, so we could create cohorts of providers for example. For studying effects that depend on the provider. Of course, you could always use their patients instead...
This question was discussed before, but I forgot in what context. The OMOP CDM doesn't care what information you have, and if it is identifiable or not. If you ask about what data actually contain - IQVIA's data have NPI and provider information.
Like create a standard vocabulary with the true providers in there? Sounds interesting, except internationally it will be a challenge. But why not? provider_concept_id=0 if you cannot link or identify.
As a world of caution: Some databases explicitly prevent you from using this information, or use in context with other information. Provider profiling will leave some folks uncomfortable. But again, those data sources wouldn't use that provider_concept_id.