As the creator of a note, I have the ability to share any note from any of my notebooks with any other Evernote user. I can even give that user the ability to edit and invite others to the same note. But any recipient of the note is only able to find the shared note in the 'shared with me' notebook. Many of the people that I share notes with have mentioned that they have their own organization structure (notebooks, tags...etc) and would prefer to put that shared note within one of their own notebooks instead of always having to find it in the 'shared with me' notebook.
I have the option to share an entire notebook, but this doesn't provide the same outcome since my way of organizing my notes may be different than another person that I'm sharing a note with. Plus, I may not want to share everything within that notebook with others, I only want to share the one note with them.
This would be similar to how documents are shared in Office 365 of Google Drive. The document itself has the share permission, but the location of the document can be adjusted by each person that has access. They can put it in their own folders and tag it however they want to. They can also find the document in a "shared with me" style folder/filter, but they have the flexibility to put the document in a place that is most helpful for them since it's in that user's own file structure.