I think many developers would opt into giving Android versions of their game to owners on Steam if they have an Android port. If this wasn't the case then some

I think many developers would opt into giving Android versions of their game to owners on Steam if they have an Android port. If this wasn't the case then something like the Humble Mobile Bundle, which regularly gives you DRM free PC\Mac\Linux + Steam keys + Android APKs would not exist. At this point I think there is a large backlog of titles on Steam that have Android ports, and like with Mac and Linux developers would add those to Steam to make their older titles more attractive to new buyers. This feature would be more of a value add to Steam making the platform more attractive. If Steam on Android was big enough Valve could capture some of the free to play market as well, you're forgetting that even though Steam sells a lot of premium titles many of the most popular games are F2P already, roughly 20 of the top 100 player count games on Steam are F2P. Valve knows how many people have the Steam app installed on Android and it's fully possible that they don't consider the effort worth it for them. For me it'd be a nice way to manage updates for games that I already own on Steam, have APKs for (via Humble Bundle), but don't want to re-buy on Google Play just for automatic updates.