The software licensing revenue is the margins. On a PC, MS would be competing with Steam, GOG, etc. for game sales revenue. The only way for them to make money in the actual PC space is via hardware margins (like Surface) or via software they publish themselves. The prospects for software licensing (for games) on PC is very low for Microsoft. For apps, they'll likely have the upper hand compared to the other PC electronic retail outlets.
On XBO, it's basically their store. You replace the hardware margins with software (games) margins. Video rental and purchase margins (again far more competition on an actual unlocked PC). As it's also still a console, the hardware doesn't change significantly for a long period of time, which means break even on HW costs at launch and extra revenue as time goes by. Not having other people building Xbox "clones" means they can keep a minimum level of quality, security, and performance. All of which are very important for a living room consumer device and not something you'd want to leave to an OEM. Unless you want the device to fail due to fragmentation, random performance levels, potential device issues, etc. that would be out of Microsoft's control.
They could, of course ditch the 5-8 year console cycle in favor of a 1-2 year upgrade cycle, but then that makes the machine far less desireable as a living room console, and we're back to why not just get a PC (spend more and have it last for longer). Right now consoles are in a nice place. You spend less, intially, to game than a PC. And on top of that, you're guaranteed a good gaming experience for far longer than a PC. It may not match a top end PC later in the generation (in price and performance), but games will be coded for that level of performance.
Like I said, there's still lots of benefits to maintaining a living room presence as a console/other device. It's yet another place for Windows to exist. Making it's overall installation base larger. Making it more attractive to developers. They'll be the only company in the world that will have a relatively uniform ecosystem that potentially works across Desktops, Laptops, Tablets, Phones, and Consoles. No other company currently has more than just 2 of those. Google has 2 devices (phone, tablets) for Android and 1 device (laptop) for ChromeOS. Apple has 2 devices (desktop, laptop) for OSX and 2 devices (phone, tablets) for iOS. Sony has 1 device (console) for whatever you want to call their ecosystem.
Regards,
SB