And risk having all those corporate drones move to Linux, Android, ChromeOS or anything non-Microsoft or, worse, Microsoft-hostile? Risk spawning a non-Microsoft ecosystem around vast IT-deficient corporations (any reasonably managed IT infrastructure has moved on long ago) that would undermine their other side businesses?
They'll never do that.
Losing those customers might be a good thing, at least if urge can still retain some business.
They gave the OS 13 years. Ask RedHat to do that. Or Google. (not even going to mention Apple for mass enterprise installations, that's not their target anyway).
Moreover, Microsoft can still argue that it's cheaper to migrate to. New Windows than a brand new system. Or you know, try to offer a VMWare or Citrix style solution to cut down on machine/licensing costs.
I've seen this experience is seen in the wider desktop space - the only time a free desktop is suitable for low support usage is when it's so locked down it's not really a proper desktop environment anymore; that locked down, it's more like an appliance. When something goes wrong with a free desktop, it's not just a matter of figuring out what went wrong, but which are the right steps to fix it. This error on Gnome, will this fix I found for Fedora work on Debian? Is the problem in Gnome desktop or in the distro?
My colleague once had a problem with something in Ubuntu, and found that there were four different solutions depending on which of the last four releases were in use. When your changing releases are years apart (Windows) this is less of a problem than when they're 6 months apart. I was pleasantly surprised when I loaded up ubuntu 14.04 and saw that it looked the same as before.
Note that I'm not in the enterprise environment, only that I've had to help a lot of people with changes from OS version to version, and understand the need for stability... which is a reason why the path Win8 took particularly puzzles me, given Microsoft's strong position in the business world. I think that the free desktops are getting there, but haven't quite arrived yet.
Where I work we have around 10k RHEL workstations, and they are all centrally managed. Users neither install nor uninstall software, they don't set up printers, they don't set up their own hardware configurations, ...
Another example is Disney animations/pixar, where all animators use RHEL workstations.
Your colleague may have given up on ubuntu because he couldn't get "desktop dungeons" or "plants vs. zombies" to run without windows, but in a coorporate setting, management does not generally consider that a priority.
Also, my colleague didn't give up on Ubuntu. He just noted four different ways to fix the given problem in four consecutive six-month releases.
She does her upgrades through the GUI (after the machine prompts her), runs mostly Firefox, imports her photos into Shotwell, shares them with her friends (on e-mail - she doesn't like Facebook), writes letters (and mail the printed copies) and seems generally comfortable with that.
She moved from Gnome 2 to Unity without thinking twice. She prefers Unity.