I have a Workspace that has 1 sheet in it. 

First:  From the sheet I shared the sheet to several individuals and 3 user groups.  All received 'Edit - Can Share' permissions.  The individuals can access the sheet while those in the user group cannot.  

Second:  From the Workspace I shared the entire Workspace to the 3 user groups with 'Edit - Can Share' permissions.  They can now access the sheet within the Workspace.

Why was sharing the sheet on its own to the group not sufficient?