If they did any research into tiling, I think a lot of their case studies would be about how to get the users to adopt and learn it. Learning a good timing WM can be very productive but you only see the benefit of it after you've already put in the work. It's not instant gratification.
Though on the other hand, MS has a habit of dumping bad UI design on the user and then having to scramble to revert amid all the commotion. Windows 8 being a prime example. So perhaps they don't do this.
There were plenty of UX studies showing that Win8 was awesome. Same story for VS 2012, another famous (at least among VS users) example - you can read the original blog post announcing it for explanations of why they thought it a good idea: http://web.archive.org/web/20140813025825/http://blogs.msdn....
It just turns out that it's very easy to bend such studies into showing what you want to see.
Though on the other hand, MS has a habit of dumping bad UI design on the user and then having to scramble to revert amid all the commotion. Windows 8 being a prime example. So perhaps they don't do this.