Valve has tried to work in the hardware space building the Valve Index, Steam Link and Controllers, trying to get up Linux Steam PC alternative to consoles. Valve also released Half-Life Alyx and also some games around the DOTA franchise. They certainly got first mover advantage with their store platform, originally to support their own games, and have stagnated since then but it's not like they're not trying new business angles beyond just the store.
Ultimately though Sweeney sees these stores that make money from third party developers in a much more direct way than just engine sales provides and he wants a cut of that market. And in that perspective none of the other aspects matters.