Companies like valve, but not valve, they deserve criticism but not this one. They have worked and invested a lot in open source projects for compatibility with windows apps and graphics performance in general.
Since videogames are very popular nowadays, their work and active support is really valuable to attract and retain users.
Microsoft owns github and google run android. They have worked and invested a lot in open source projects except they do it only out of convenience and it's just a fraction of what they actually do. Making proprietary software available for linux only extend companies reach.
Steam policies are against everything linux stand for. It's a closed source third party launcher where they rent games under DRM and steal all sort of data while doing so. Valve created a small monopoly in wich videogames makers are abducted in routing their games through their useless launcher to get some visibility. They also abducted people to install their proprietary app to play certain games.
I've read it. Nothing prescribes a foss philosophy outside of Linux itself. Or for that matter a dickhead attitude to those who don't subscribe to one.
The only open source and DRM free way to get games is by pirating them. That's not Valve's fault, that's the fault of the current copyright system. It would be nice if the Steam client was open source but that's also about all they could do. Banning DRM on Steam would just lead to big publishers using their own launchers exclusively and indie games don't use DRM anyway. Let's also not forget that Valve is contributing a lot to open source projects.
Valve pushed drms on the game industry, before they monopolized the market you used to buy the cd or install a game without the need of a useless proprietary launcher