There may be issues with Steam's hold of market share (or not), I won’t debate that. But I don’t think it’s comparable at all to the topic at hand. If you want to sell a video game to PC (personal computer, not necessarily Windows) users, there are many options besides Steam and Steam has no special position of privilege on any platform it's available on (Windows, Mac OS, Linux). You could still distribute your game by CD if you wanted to and it would work as well as any game bought on Steam. There are also many other digital games distribution platforms. They may not be as popular as Steam, but Steam has no inherent advantage over them. On a Windows PC, for example, Steam has no advantage over Origin, or GOG Galaxy, or any other.

Its popularity is due to other factors, not some privileged position it occupies. Unlike Google’s or Apple’s app stores which absolutely have a privileged position on their respective platforms.