Please allow them, for some reason github, photo bucket ones are allowed but not Google drive.
For anyone that has no idea what I am talking about when you click Image and add an address that is the permalink of that image.
you can do this from Google drive to (if you allow public access) this makes life easier so you don’t need to use photobucket for image hosting, and Google drive for file hosting etc…
You can use gdriveurl.com , it got updated and now allows users to log in with their google drive account and share the list of files instantly, getting for each file " View" & " Download" short permalink.
There’s also the old solution (login to Google Drive, set everything to “Public on web”, copy share link, convert it into the gdriveurl.com textarea in the homepage), but it’s just a waste of time, you should try “MyDrive” api.
You should write a post about it. It’s more user/mobile friendly and complete.