People use capitalism to mean anything involving commerce, I guess.

The fact that valve is privately owned and the profits go to the owner instead of the labor isn't really the reason steam is dominant. A worker owned co-op could have succeeded by making the same product. Though if they were beholden to shareholders who demanded a profit, it probably would have resulted in a worse product. An argument against capitalism, with uninvolved owners taking profits, if anything.

They made a product people like. Boo-boo. Epic could have made a good product. They didn't.