TL;DR: The Graph needs a specific permission to delete Teams, instead of Group.ReadWrite.All.
A while ago some new Teams specific permissions were introduced to the Graph. Because of this an application can now manage Teams without the Group.ReadWrite.All. Except for one thing.
If the application needs to be able to delete a Team it still needs Group.ReadWrite.All.
Example:
We have an application that manages Teams. The customer doesn't want to give us access to all groups (understandable), but we need to be able to delete Teams. This requires the Group.ReadWrite.All permission, which enables us to list and manager ALL groups within the tenant.