Can someone please explain Warner blocking certain characters from tv appearances?

I just read that Harley is being blocked from appearing on either "Arrow" or "Flash". I also know that Ray Palmer/Atom was originally going to be Blue Beetle. Finally, we know they can't show Supes, Bats & WW.

So here is my question...Why? It makes no sense. Warner has said both its tv and movie verses were separate. So why not allow any of these characters from appearing.

Has anyone from Warner or the production teams answered this question?

Thanks!