> Valve killed the previously thriving boxed game industry two decades ago

Boxed PC games were practically dead by the time Valve started selling 3rd party games on their marketplace. Most game stores around me had stopped selling them or massively shrunk the shelf space for them. Xbox, Gamecube, Playstation 3, they had whole walls of the store dedicated to their stuff. PC games had a couple of shelves in the middle of the store, if even that. Sales for PC games had massively fallen between 1999 and 2005 while the rest of the game industry exploded.

The industry had shrunk over a third in five years before Valve started selling online. You can't say it was "thriving".