You don't have to buy MS hardware to play their first party games. That's the point.
To which MS doesn't care, they just want you in their ecosystem. They don't care if you're on PC or on Xbox. They are giving options to more people this way instead of just making them buy their 1 box.
Does this reduce the amount of consoles sold? Sure, but again as long as you are buying their games within their ecosystem, it's clear MS does not care where you get it from.
edit: Surface for example, will never beat Apple's #'s, but MS is making a lot from that device despite that you can get almost everything on it also on your PC through the Win10 store. It's options.