Steam still has to deal with Epic being willing to throw billions at trying to dethrone Steam, and Gog being alive and well and being in the perfect position to say "we told you all along that you shouldn't have to trust Steam, buy your DRM free games here". Also every big publisher wanting to pull their own games to their own storefront and only being forced to crawl back because gamers refuse to leave Steam

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)

One point in Steam's favor (not to suggest that Valve is above reproach) is that it doesn't impose any DRM. If games have DRM, that's the publisher's decision.