I don't think this tracks. Steam's model is developing software to automate or crowdsource expensive effort. Now, anyways. It originally was to fix PC piracy, but they achieved that ages ago.

And hell yeah they have a natural self-reinforcing monopoly. Even ignoring the mass of captive users with tens or hundreds of thousands of dollars committed to the platform, Valve has been doing feature work on that storefront for decades. When others try to compete people immediately bring up the expansive value added features. They make their own controller drivers. They make their own compatibility layers. They make their own OS, FFS. In what world bringing a PC storefront to that level would "not take much"? It's an Apple-style ecosystem model, and much as it terrifies me that it's an ever growing monopoly, it's still impresive that they managed to build it within Microsoft's own.