I know people like to throw around the word monopoly willy nilly because it definitely is easy to conceptualize and puts up a certain mental image, in some ways you could argue steam indeed is a monopoly, but the issue with monopolies, especially the ones that are organic or natural and not the result of market manipulation or horizontal/vertical consolidation is that they have to act a certain way to be punished. Steam doesn't engage in anti-competitive practices, and doesn't meaningfully use its market leader position to damage competitors or consumers.