What Valve want is the dissolution between platform/architecture and store. By my eye, it's the driving force of their efforts, more so than them selling hardware or being the open source good guys. Not to undervalue their work in helping make Linux a first class citizen for gaming, but the core of their business model is getting people to engage with their store, full stop, and being able to sell their games on Android (and elsewhere) would massively extend their reach.

This may go both ways too, there's also been indications that Valve have been tinkering with Waydroid, meaning Steam could also become a store for Android-native games.