Dartpaw86: Are they just abandoning it?
No idea, but most likely no.
Dartpaw86: Was it actually unauthorized to begin with and Steam shut it down?
Steam has nothing to do with it. GOG used the Steam API to poll a user's games, and the publishers that wanted to participate told GOG that they could offer games X for free.
Dartpaw86: Just not gaining enough interest?
What kind of interest? It was a limited time promotion, and whether or not it was a success remains to be seen. I do believe we'll see more games coming to GOG connect in the future, but again, for a limited time.