That's kind of unfair for those who paid for the game here. May be you can update the game without Steam features? Not everyone needs multiplayer.
The steam api is integrated into game. The api protects the game against distribution to other platforms and adds functionalities to it. I thinks it's also against the legal agreement to put the game with the api in this store. However, since you can claim a free steam key on this platform its not that unfair.
> The api protects the game against distribution to other platforms
Well, I bought the game on itch.io because it was DRM-free. It's a feature for me, I don't use DRMed stores at all.
> and adds functionalities to it.
What do you need it for, besides for multiplayer? It's a pity you need to rely on lock-in functionality which prevents you from releasing the game in DRM-free stores.