Microsoft doesn't withold OEM licenses from competitors. That wouldn't make sense for a number of reasons. 1. Microsoft doesn't license xbox software, so in th

Microsoft doesn't withold OEM licenses from competitors. That wouldn't make sense for a number of reasons. 1. Microsoft doesn't license xbox software, so in that regard a Valve Box isn't a direct competitor. 2. Windows and Xbox (Entertainment) are separate business units, with different revenue targets. 3. Xbox is far from the market leader in the current console generation, and hampering Windows sales to boost Xbox won't make up the difference. 4. There doesn't exist a relationship that can't be forged by increasing the how much you pay. Said plainly: if you're willing to pay, Microsoft will do business with you (governments and legalities aside). To the original question, why Valve does anything is a mystery. Speculating: This is laying foundations for streaming games as a service. Linux is their target platform for the game servers. I don't believe this is about top-line revenue, as PC Master Race has overwhelmingly chosen Windows as it's OS, and it's not going to change. Edit to Add: Actually as I think about this more, the central motivation is even more simplistic: a group of valve employees wanted to make more games compatible on Linux. Their entire driving force is doing stuff they find interesting, as long as it benefits the customer. There exists Valve customers who can't play games, because they're not available on Linux. Thus, Valve is addressing it. Valve has so much capital resources, they're not motivated at all by financial reasons.