Games are exclusive to Steam all the time, it's just that Valve doesn't have to pay for this luxury, they just *are* due to the first mover feedback loop that Steam enjoys (everyone uses steam, so that's where the buyers are, so games prioritise intergration with steam, so people use steam because that's where the games are, so everyone uses steam, etc).
Is this a weird pretend way of saying Steam without saying Steam? Or do you actually mean that it's on Steam, GoG, Itch, Windows Store and DRM free on the publisher's website?