It's not as simple as that. Sure, she can do that if all she wants to do is copy it once. But what if the folder's contents are frequently being changed and s

It's not as simple as that. Sure, she can do that if all she wants to do is copy it once. But what if the folder's contents are frequently being changed and she wants to keep Bob abreast of them? If files in it are being changed, and new ones are added? Then she has to make the effort to track changes and repeatedly email them to Bob. It's a matter of the amount of friction involved, and there can be a big difference in friction between being able to share-by-copy things and just giving access to the folder.