I would love to see an analysis of how valve's openness and goodwill affects their bottom line. Intuitively it should be a net positive for them, but there gotta be upfront costs, otherwise everyone would be doing it too.
A better way to look at this is valve is trying to hedge it's self against microsoft. By creating an ecosystem of devices and software that's full open so they're not reliant on Microsoft. The goal of Valve hardware ISN'T to make money. It's to encourage others to build devices free of Microsoft that Steam can be installed on.
They have nothing to gain by being closed, and everything to gain by being open.
Efficiency is not a word I would use when speaking about rent-seeking. Landlord that 20 years ago bought some land that later became valuable and who is today renting it out is infinitely efficient as they are doing jack. And amount of respect they get is about equal to their economic output.
Same with Steam. You are absolutely free to sell your game not on Steam. Except that unless you're a super massive giant selling highly anticipated game you might get no sales. But the choice to eat or starve is always up to you.
Steam has been an incredibly good steward of its position, but I fear for the day when capitalism finally sinks its claws into the platform.
Capitalism has nothing to do with short term greed.
Some CEOs are just too arrogant and think that optimizing for the short term won't hurt goodwill. That's their own failure. Capitalism says nothing about how a business should be run. It's merely defining the idea that humans who own things (capital) allocate their resources and keep the result.
Regulation can also break things if done incorrectly/poorly/inefficiently/corruptly.