*snip everything you've said in the thread so far*
Valve isn't structured as a PC games publisher. Publishers aren't just moneybags. They have a ton of support teams working to maximize the potential of their investments. They have PR teams, marketing teams, QA/CS support teams, developer support teams (including design, art and engineers), financial departments, legal teams, production assistants, and a laundry list of third party companies who offer a plethora of services to their first party studios.
Valve doesn't have that structure, even as developer who self publishes, they still rely on outside help from publishing partners for much of the above. Building that structure is an incredible investment of not only money, but also time, people and expertise.
Valve doesn't have the same investment return as a hardware manufacturer. They don't need to bring people to the PC platform because they don't sell hardware. And they don't need to bring people to the Steam storefront because they already have a soft monopoly on digital distribution of PC games. First party games from console manufacturers are often not very profitable themselves. Even when a first party title is wildly successful, it will still make less money than a multi-platform release simply due to the limitations of releasing on a single platform. This risk is offset by the hardware manufacturer by the increased hardware sales said first party title may generate. Console manufacturers are willing to make less profit per individual game
(even sometimes take an overall loss) if it moves more hardware units to end users, generating a larger user pool. Because console manufacturers aren't only making money on each individual hardware unit sale - they also profit from licensing fees for each game released on their platform as well. So, they have double the motivation to move units - both from a direct sales perspective and from making their platform appealing to third parties to gain licensing fees and have better negotiating positions for exclusive content.
Valve has neither the offset of hardware sales or the offset of licensing fees to reduce the risk of taking on the role of a first party publisher.
Valve makes substantially more profit from being a storefront with substantially less risk than they do from being a developer or publisher. You asked how anyone would know their ROI would be low unless they tried. Well, they have tried. Valve has a storied history of acquiring products, often in various states of completion, for exclusive release on Steam. And the biggest reason you've seen a dramatic slow-down of that type of development and acquisition is that... the Steam store makes more money with basically zero risk. Valve has shown they have very little interest in taking on major risks anymore. Everything they've done for the better part of a decade has been to move away from risk and liability
(moving all of their systems onto the users) and focusing on tried-and-true sequels and games as a service. And you can't really fault them for doing so because it works. It works really,
really well.
Your assumptions about Valve seem based on the idea they want what's best for PC gamers when that's never been demonstrated. A lot of their policy changes appear to benefit their users, but often are a much larger net benefit to their profitability margins. Which, hey, if you can do both, more power to you. But that's given people the idea that Valve will be willing to do the same
(do what's best for their users) when it clearly doesn't benefit them financially to do so. And that's never been the case.