Has it really been that long? Apparently so. Valve originally announced their rebranding of Steam Play with Proton back on August 21st, 2018. Seems like a good time for a quick reflection being halfway to a decade old now with the tech that gave rise to the Steam Deck.
I think their efforts are more for bringing gaming on Linux to more mainstream attention. Not knowing you can game on Linux is a major factor for a lot of people in not switching.