Again, Steam only gets a cut from games sold on steam store itself. This is not a matter of guessing, it is a fact:
Also: a look at the top game legal trends of 2023 & lots more...
newsletter.gamediscover.co
And look, Sony is actually selling their games via Steam keys on its own site and getting 100%, but I guess few people know about that
Join the Helldivers and fight for freedom with friends across a hostile galaxy in this fast, frantic third-person shooter.
direct.playstation.com
The epic Horizon Forbidden West in its entirety, including bonus content and the Burning Shores expansion.
direct.playstation.com
Fair enough. I wonder what Valve gets out of this. Pretty generous just to allow publishers to bypass Steam commission like that. Also, what I don't understand is that it stresses that Steam customers must get the same deal as the keys sold elsewhere, but we know that it is common for this to not be the case. I bought GoT on Fanatatical for $10 less than what it was being sold for on Steam. Maybe Valve isn't monitoring very closely? Not sure.
Edit: Looking at the Steamworks page, it seems Valve will typically approve additional steam keys as long as the publisher isn't trying to entirely bypass the Steam system. So I think you were right when you said this was being used to drive folks to Steam. Valve is going to allow free keys for publishers as long as there isn't a major "imbalance" in the number requested versus the sales of the game on Steam.
"When reviewing Steam Key requests, some of the things we typically look at include the level of customer interest on Steam, the total number of keys that have been issued and activated for the game and the additional number that are being requested. A request will usually be rejected if there's an imbalance that suggests the developer is not making an offer to Steam customers that is comparable to what Steam Key purchasers are offered. For instance, a game with a few hundred units of lifetime sales requesting tens of thousands of keys, or more."
partner.steamgames.com
Clearly my "guess" was entirely wrong.