Why are Xbox and PC gaming still separate?

I really hoped that by now I'd be able to buy a game once and play it on either my PC or my Xbox One. I'm just confused by this because Microsoft made a huge deal about how the Xbox One ran Windows, had a x86 architecture, could download apps from the Windows Store, and uses cloud saves; not to mention the fact that the Xbox One controller now works on PC's and they just announced Kinect 2 for Windows.

I feel like Windows 8 should be able to run Xbox games with achievements and all (a great replacement for Games for Windows Live) as long as the hardware is at least as good as the Xbox One. Developers could target the Xbox One as the baseline, and leave in the higher level settings for more powerful PC's.

Most importantly I'm just tired of watching all these Xbox One exclusives get pumped out while Microsoft continues to ignore PC gaming that they claimed was incredibly important to them. For example, I'd really like to see Halo: The Master Chief Collection be playable on the PC; I'd even be willing to keep paying for Xbox Live!

Am I crazy?