Besides second order stuff like that it might help some Steam Deck sales (mostly by demonstrating their commitment to the platform and attract other companies to develop for it, moreso than anybody rushing out to buy a Steam Deck specifically to play Half-Life), the fact that Valve does stuff like this that's not directly "make all the money right this second"-driven is in no small part why Valve has such goodwill with the PC gaming community.
In theory, it's not that hard to compete with Steam. Valve's cut of game sales is massive, and a competitor could easily slash into that to undercut them. Which is what Epic Games is trying to do. Yet, Valve maintains an extremely dominant market condition largely predicated on that goodwill.
And, of course, exactly because of that dominant market condition, they've got all the money they could possibly want to burn on random vanity projects.
Well it's not exactly trivial to build a software as extensive without just being a rip-off and having the share of games at launch. Gamers are extremely picky and it costs tons to build out a scalable system. This is where Epic failed. Sure they gave me a ton of free games, but their UX was horrible that I just never went to it and stayed within Steam.
Epic launcher actually randomly crashes my display window manager from time to time, I just can't have it running in the background as I do with Steam.
In theory, it's not that hard to compete with Steam. Valve's cut of game sales is massive, and a competitor could easily slash into that to undercut them. Which is what Epic Games is trying to do. Yet, Valve maintains an extremely dominant market condition largely predicated on that goodwill.
And, of course, exactly because of that dominant market condition, they've got all the money they could possibly want to burn on random vanity projects.