Why this game don't have cross-multiplayer ? This isn't acceptable :S Wasn't it purpose of Galaxy ?

As far as I can tell, Galaxy's plan was cross-platform multiplayer, using something open to connect with. But if the game was built for Steam I'm guessing they'd need to redo the entire connection stack, as they're using the Steam stack for that bit.

Kinda wondering whether "Does not connect with Steam" also means no multiplayer with non-steam (as in no-netplay) or it just means you can't talk to Steam clients.
In case of the latter I think I'd be okay with that. Maybe at some point the Steam version could contain support for both Steamworks as well as non-steamworks multiplayer. Though if the Steam version gets smaller point updates making the game incompatible with non-steam versions for multiplayer anyway, I'd fail to see the point.

The steam also doesn't use room codes, the gog one does. It uses multiplayer servers

OP's post should be reverted since things have changed back to abandonment by devs.