Supporting external identities would improve the 'users outside your organization' use case
Azure Virtual Desktop architecture recommendations - Azure | Microsoft Learn
Users outside the organization will already have their own identity, either in their own AAD (Entra) tenant or with another provider.
Azure Virtual Desktop should support external identities because:
as an application developer, managing their identity is not something that adds unique value;
as the end user, I don't want to remember another password.