Just like Sony has a monopoly on PlayStation OS gaming, Microsoft oddly enough has a monopoly on Windows OS gaming. Except Microsoft doesn't extort game publishers that wish to publish games on the Windows platform. Ooops, I meant charge a license fee in order to sell games on their platform. For that they have the Xbox OS gaming eco-system which they have a monopoly on.
Along those same lines, Apple oddly enough has a monopoly on iOS gaming as well as MacOS gaming. And Google has a monopoly on Android gaming. And Nintendo has a monopoly on Wii OS gaming. Etc...
So, er... What's your point?
Both publishers and consumers have a broad range of choices for gaming platforms they wish to support.
Valve is attempting to create another gaming OS ecosystem that they will have control and thus a monopoly over. But it's still in its infancy and doesn't have a great chance at success, IMO.
What is interesting is that out of all of those above "monopolies", only two ecosystems are "free" to game developers. Windows OS gaming and Mac OS gaming. As well as a third one that wasn't mentioned. Linux OS gaming. Steam OS just like the consoles, iOS, and Android charge a fee (per sale) to the developers. Although for Android, if you sell only to rooted devices, then you can bypass that I suppose.
Windows OS gaming remains as popular as it is because it's a well supported platform to develop on that has robust support for gaming across an extremely large install base. That extremely large install base is the only thing that makes it profitable despite the rampant piracy. If it was the bastion of tyranny that you would like to imply that it is, then Windows OS gaming would be dead as publisher's and consumer's wouldn't support it.
Regards,
SB