i posted the question in steam and got this answer from a developer, see attached.
It's gonna need more votes: https://www.gog.com/wishlist/games/lucius_2_the_prophecy
But honestly, I wonder if there's some other reason, maybe something technical related, or even a legal issue (like if the game has content that would cause it to be banned in some other countries or something).
Another thing that's bothersome is that the original got a lot of updates on Steam, and not many on GOG.
I actually liked the first game, so I'm still hoping the second one will come someday.