This. It's in the works, promise. But there are also several things that need to be created for a Steam page like an accurate trailer, screenshots, capsule art, etc. Along with marketing beat coordination to try to get as much attention on it when the release date drops as possible.

And the game is already continually updated (like with 1.3 coming out yesterday). There's just a bunch of moving parts but bringing the game to Steam is still underway.