Exactly. I understand the simplicity and convenience of console gaming (I bought an XB1 a couple months ago simply because there are just some games that don't come to PC). But at the same time, I think most people have been brainwashed, or just don't know what a different universe PC gaming opens up. If you're a dude-bro and you only like shooting things and sports...then yeah, you can't go wrong with a console (and you're probably unlikely to be able to grasp some of the intricacies of the PC world anyway...maybe that's not fair, but in a lot of cases, it's true).
The dude-bros and the soccer moms buying for Little Timmy is where the console world's bread is buttered. Microsoft, Sony, and even Nintendo makes a FORTUNE off these people. They either don't know or don't care (due to difference in cost) that the brand new, "next gen" hardware they just bought is on par with what PC was doing three years ago. XB1/PS4 are struggling to do 1080p at a consistent 60 frames per second (with many games even missing that mark).
To give perspective...the most recent development kit for the Oculus Rift needs a machine that can pump 1080p at 75fps to be used properly. And that's not even the consumer version. So, how in the hell Sony's Morpheus headset is going to work, I have no idea. I realize the full potential of the system hasn't been tapped into yet and breakthroughs in rendering techniques can happen...but still, they've got a lot of ground to cover.
So, to address the exact question of why doesn't Microsoft turn the XB1 into a "Steambox"...because it would kind of be a shitty Steambox. I mean, for a pre-built unit, and what you get for the price, it's not terrible...but I think most people interested in PC gaming would want more. And for the people not interested in PC gaming, it already does what they need.