Why can't some contacts be moved between accounts? Using the El Capitan Contacts app, I was able to drag and drop several contacts from an Outlook account to a Google account. However, there is one contact that I am unable to drag and drop. It has a bit more information than the others did. The green plus sign does not appear when I drag this contact over the Google account, but that green plus sign does appear when I wave this contact over an iCloud account and another defunct Exchange account.

What is it about this contact that makes it different, and what can I do to drag and drop this contact from my Exchange account onto my Google account?
I report here my comment above.

The reason why you can't move the contact to Google (why you can to other accounts) is that this card is already present in Google.

If you look at the "cards" section of the contact, you can see all the accounts that contact is synced with.

 

Therefore, you can just drag and drop the contact to accounts that do not appear of that list.