I remember reading you can only generate keys for a product that is or has been on sale through the Steam store
Steam Keys (Steamworks Documentation)
partner.steamgames.com
Relevant portion:
My guess is as a result of their deal with Epic, they are going back on their distribution agreement as the game will never be distributed on Steam. Who knows, this is uncharted territory and I'm guessing special considerations would have to be made if Deep Silver even attempted to approach Valve about this, but I see zero reason Valve would want to be amicable in this scenario.Crowdfunding.
Keys can be used to fulfill crowdfunding rewards and grant backers access to your product. Providing backers with beta testing keys prior to release is also OK, but only backers should receive those keys --they shouldn't be sold outside of the crowdfunding campaign unless your beta is also available for sale via Steam.
Steam keys can only be promoted as a reward for products that have already confirmed Steam distribution -- it's not OK to use the Valve or Steam logos to market a product that is not currently under Steam Distribution Agreement. For ongoing crowdfunding that does not have a set end date, it is only OK to sell Steam keys if the product is also available for purchase via Steam at no higher than it is offered via your crowdfunding campaign. If you are selling Steam keys for a beta or early access version of your product, you must follow the early access requirements listed below.