Why isn't Vampyr available to pre-order and download on Xbox One?

It's available for preorder in retailer here: http://www.vampyr-game.com/shop

Xbox Store preorder will arrive soon.

It's also not available in some countries yet .... here in Portugal i can't pre-order it in any shop yet.

It depends on the retailers. It will come eventually. Sorry for the delay!

It's okay, it's worth waiting for haha