Why cannot I move an entire private folder with contracts added to it into a shared folder? 

It is not possible to achieve this in a single step. 

If you have a Private folder with contracts and would like to add it to a Shared folder and share it with your collaborators, you have to go through the following steps:

• Create the Shared Folder you want to use. 
• Open the private folder and select all contracts you would like to move to a Shared folder.
• Add the selected documents to the Shared folder you have created.
• If you do not want to keep the contracts duplicated in your private folder structure, delete the private folder.
• Open the shared folder and select the collaborators you would like to have access to by Sharing it with external parties.

If you want to Move a Private folder to another main or subfolder from your Private folders, you can do that in a single step: