People-reference anatomy

The diagram shows the universal three-step shape of any people-reference in Power Automate - the raw identifier the source row carries, the profile record it points to, and the actual email you reach via an Office 365 Users lookup. Dataverse uses a GUID, SharePoint uses a Person object, Salesforce uses a Lookup ID, and Excel often uses a plain email string. Same three boxes, different labels.

Study the three boxes, then answer the question below.

Why can't Theo just drop the ResponsiblePartner column directly into the email's To parameter?