Valve is just hedging against Microsoft having a big red button to kill Steam. They've built their kingdom on top of Microsoft, and Microsoft would love to have it for themselves I'm sure. It's in Valve's best interest to divorce themselves from Windows to protect themselves from Microsoft.

It happens to also benefit the Linux gaming crowd, but it's still ultimately self-interest driving the work. The engineers doing the work are probably doing it for the altruistic reasons, but ultimately Valve is writing the cheques.

No, I think Valve prioritizing an open platform independent of Microsoft aligns with their business goals.

They’re doing it in a manner that has broad benefits, but it’s definitely a win-win situation.

Not at all, they don't want to pay for Windows licenses, as seen there is very little incentive to actually support native Linux games.

Additionally they want to prevent losing Steam content to Windows Store or XBox PC App.

If they could get Windows source at zero cost, like the Netbook OEMs did in the early days, they would quickly forget about Linux.

Additionally, don't forget current Valve's management doesn't live forever like any of us, and who knows what will happen to Valve afterwards.

What makes Valve great at the moment is that their business interest often aligns with ours (e.g. on the Linux support front). Which is great, don't get me wrong. But that's still beneficial for the company.

It's in Valve's interest to have their own OS and not rely on a rival's platform. Especially a rival that has proven many times they WILL abuse their power.