It might be me, but I just don't feel the PC platform is comparable enough in market philosophy to consoles to even warrant concern behind "Xbox exclusives" making their way to both services instead of just the one.
Microsoft/Sony/Nintendo exclusives make sense as business as you the customer are buying into a locked hardware ecosystem financed and controlled by the parent company. You adhere to their rules, their services, their design, and in return receive access to buying exclusive software. Buying an Xbox/PlayStation/WiiU is like buying a hardware license to further purchase very specific software. Ergo the bread and butter of this business, that being gaming hardware, is to provide said software as exclusives to tempt a long term investment in the hardware itself.
The reality is that PC is not comparable as it is not a locked or controlled ecosystem by nature. Specific services within the PC ecosystem can be locked and controlled, but that's the point; they're optional and this itself is the competitive business. Sony/Microsoft/Nintendo compete with hardware space via software. The PC business is different, and instead publishers generally compete with services via software. And these services can be applied to any number of hardware configurations and designs that do not benefit the service provider/publisher with a monetary return.
Microsoft wants you to buy Quantum Break on Xbox One, because the assumption is that if you buy an Xbox One you probably game a lot on consoles, and they want you gaming in their console instead of the similar PlayStation 4 ecosystem, given a majority of software is a crossover between the two. Meanwhile people who game primarily on PC generally don't see the consoles as competitors, but instead a separate ecosystem. They might buy an Xbox One exclusively to play Quantum Break, but that's likely going to be where it begins and ends, sans other Xbox One exclusives. In short, they won't buy into the entire console software ecosystem, as they're already invested in one.
By providing "Xbox One exclusive" games on PC they are competing as a service, not as a platform, in an ecosystem that is all about services and not platforms.