HIPAA services are not separate. You only need to establish a Business Associations Addendum (BAA) with AWS and stick to HIPAA eligible services: https://aws.amazon.com/compliance/hipaa-eligible-services-re...

GovCloud exists so that AWS can sell to the US government and their contractors without impacting other customers who have different or less stringent requirements.

Product segmentation. Certain customers self-select to pay more for the same thing.