Did you fill out the age rating form in the Steamworks for this game? Shouldn't take that long and will cost you no money.
For example in Germany all games that have yet not managed to fill out their age ratings on Steam get automatically blocked as well as 18+ adult games (sex). This could be simple puzzle physics games that wouldn't need an age rating, but due to laws in Germany everything requires and age rating. Steam just then block a game for my region if no age rating was provided by the developer/publisher. Region access will then be unblocked if the age rating was provided and reviewed.