FTP acces to WebDAV?

I’ve read through many of the posts on here regarding WebDAV. Everyone has made it very clear that if you setup a WedDAV folder that it will not be accessible via FTP. Now the question is, why are certain sub-folders in the WebDAV root folder allowing me to access them via FTP while others do not? I had assumed that NO folder would allow me to access them via FTP. I ask this question because we would like to backup the folders we have on our WebDAV onto our internal backup system. Your help will be greatly appreciated.