We've reached a sort of gaming singularity where nearly every video game can be run on any hardware you choose or be streamed over the network to a thin client. PlayStation and XBOX consoles are basically dedicated gaming PCs that can only run Sony or Microsoft's version of Steam. DirectX is losing ground too thanks to Proton and Vulkan, so Microsoft won't have the last laugh there either. If Valve controls the store you purchase games from, the software which runs the games, and the operating system running the software, they are an ODM contract away from becoming Sony's PlayStation division, and look where they are now.
And even if they somehow arrived in a market position where being less benevolent would make more money: Valve isn't publicly traded, nobody is forcing them to make the most profitable move. As long as Gabe and the other owners prefer being benevolent they can continue doing it
(not that they are all around benevolent. "consistent" and "usually choosing the side of the customer over the side of the publisher" is maybe the better framing)
Now if the RAM companies make it so you won't ever be able to afford your own hardware and every game company pushes cloud-only gaming... Well, we aren't there yet thankfully, but I fear it'll happen.
Gabe seems like the kinda guy who is in the Game for the love of games.
It would be a legendary legacy indeed to commit Valve and it's profits to a trust which defends digital rights and freedom.