Hi Pav, this is by design. The REST API keeps subscriptions and contacts as separate resources, so contact fields such as name and email are not included in the subscription resource.
If you need contact details, you can use the contact_id returned by the List Subscriptions endpoint and retrieve the corresponding contact through the Contacts endpoint.
I’d also suggest reviewing the available documentation and endpoints before reporting items as gaps, as the required information may already be accessible through the existing API design.