Not free... They're a business.
They're a business, so unless they can make up the shortfall from other sources, free giveaways isn't an option - even though that's what got MS Windows popular to begin with (albeit a bit without official permission).
But, say, a price of 20-29 pounds (above 29, even if it's 29.01 or 29.99, and you lose me), and I'll buy it when I need it. And I'm not using Windows except in a virtual machine, when I have to run some Windows software to configure some hardware, and I have no Linux option. I have a Mac as well, so I don't boot my XP VM very often at all, as most Windows software houses also publish for Mac. I paid 22 quid for my XP (retail French edition, regeditted to accept the English SP3, so now it's a mix of languages, mostly English, but still with some French in it). And then MS didn't get a single penny out of my 22 quid because they're not selling anything in that price range. I'm OCD enough to avoid pirate software unless there really isn't any other way to get the job done for that throwaway case I can't use Linux for (which means paying lots of cash for software does not make business sense). I haven't pirated anything in many years by the way - the one case that may have required a pirate copy came with a trial version of their software - and I ended up not using it anyway, because it didn't suite my needs (was beaten by vim if you can believe it).
I paid 13 quid for a OS X update after I got my used Mac without batting an eyelid, because friggin' Xcode wouldn't run on 10.6, and I needed Xcode. To me Mavericks really is free :) When I do need to be reminded of the stupid OS that is W8, I boot an image from modern.ie in a VM - none have survived more than 4 hours so far. And I'm an avid Ubuntu Unity user (in 2D, with XfWM instead of copiz or metacity - those are slow as hell), which as far as I can tell receives a lot of hate...