Moved their forum to Steam?
Yes. Their reason was it was taking to much time from working on the game to keep two forums running. Since most of their customers were from steam they would archive their forum and use steams forum as their own.
That wouldn't qualify the game
for this list, though. Besides, what about all the (many) other devs & publishers who have never had their own dedicated forums at all (and have thus probably been using Steam Community all along), or who have shut them down/transferred them to another service (Steam or otherwise)?
"Developer moves their customer forums from one site that's not GOG to another site that's not GOG" is not, by itself, a very good criterion for inclusion of any of that dev's games in this list of shame, IMO.
(And be real -- would you really want anyone to voluntarily inflict GOG's
forum software upon themselves as a medium of communication with paying customers? I hang out here for "amusement", not business -- though there's little enough of the former these days -- and I can hardly be bothered any more to keep up with what has broken most recently, or what Byzantine workarounds have been uncovered just to let us do the most basic things we used to be able to do.)