Steam is made by Valve, and Valve, dispite their many failings, have shown a very strong commitment to FOSS.
Their contributions to Proton have played a massive part in making Linux a viable platform for gaming. Without them, Linux gaming would be stuck back 10 years at least. Back to the dark days of naked Wine and fighting with configs for hours just to hope to launch a single non-native game.
Valve has also locked themselves in with the Steam Deck. By creating a fresh hardware platform based almost completely on a FOSS software stack and by making it open, moddable, repairable, and upgradeable, they have made it very tough for themselves to break away to a proprietary solution further down the line.
All these things cause me to trust them quite a bit. Make no mistake, I’m committed to FOSS first. If and when Valve goes down the enshitification path, (once Gabe dies, sells out, or otherwise passes the torch), I will move off of the platform and only use FOSS games/software and resources like Lutris, Bottles, GoG, etc.
But until that dark day, I will support Valve at least passively. because by committing to so much development towards FOSS platforms, they are locking themselves into it and proving to us that they aren’t just giving lip service to the FOSS community.
I wish Steam was FOSS, I wish Steam wasnt DRM itself, but in a world where things are mostly grey, I personally feel comfortable currently supporting them with my money.