This is a different store. If it doesn't say you get a copy on steam then there's no reason to believe you should get a copy on steam via an itch purchase. Itch is better than steam anyways. You get it DRM free, (which means you can launch it in steam if you really want) you can keep it up to date via the itch app, and you get to more directly support the developers. What more do you want? What does steam have that you can't already do with this version of the game?