Inter-Region access to endpoint services

VPCs are regional constructs, and so are VPC endpoints. A VPC endpoint can only be created in the same region where the resource used to deliver it (NLB in this case) resides. Even more specifically for VPC interface endpoints, the ENIs of the endpoint must each reside in the same availability zone as one of the ENIs of one of the NLBs used to provide the VPC endpoint service.

You can, however, access a VPC interface endpoint in a remote region over an inter-region VPC peering connection (or several other means), and that's the scenario illustrated in the diagram.