Kikinaak: "totally understandable" only to those who dont know much about programming. It takes a bit of work the first time to include either steams stuff or gogs on a build switch, but once thats done its automatic from there on out. This dev is already building windows, linux and mac binaries. Next to that, this is trivial.
He had a demo available here, so there can be no argument he cant build for gog because he has done so. I dont know exactly when the demo was pulled from gog, but I suspect it was when he sold his soul to Paradox. He has given a "not before 2 years" estimate when asked on the steam thread about a gog release eta. Thats 2 years of free advertisement hosted on gogs dime and bandwidth while the dev profits elsewhere. Gog should not tolerate this, and customers should not financially reward it.
This. I can't say better. If the Dev (Or Devs) wants to stay with Steam, go ahead, but the GOG users (And GOG itself) should not support that choice, because now is the Early Access game, and - if is - when it will be released HERE, the updates, DLC's, or bug patch, like other games abandoned by it's creators.