@Chronos
Why?
Frankly, I don't give a rat's ass about market share. I do, however, care about my own time.
My 90+ yo Great Aunt, running the variation of the Slackware 12.2 distribution that I originally built for my Mom, hasn't called me for computer support in over 10 months. Prior to that, I'd get calls to "fix my Windows, please" a couple times a month. These days, the wife & I make the three-hour round trip drive a couple times a month for tea, instead of to fix her computer. Much nicer.
The kicker is that she's turned a bunch of her aging friends on to Linux ... to them, it's "the version of windows that Martha's nephew gave me" ... I've tried explaining that it's not actually MSWindows, but they aren't really equipped to understand the distinction ... and frankly, it doesn't really matter, when you think about it.
When properly set up, Linux just works. When set up according to the manufacturer's suggestions, Windows is an accident waiting to happen.
Note that I'm no fanboi, I have Microsoft, Apple, IBM, HP, Sun, Linux, BSD, and etc. products running in my machine room as I speak (including archaic & obsolete stuff that I need to support my customer base ... DEC Tops-20, anyone? How about Tandem? Amdahl?). All of them have their uses, and they do what they do as well as can be expected.
None of them, not a one, combines the stability, ease of use, security, scriptable remote maintainability, and hardware compatibility of a properly setup Linux system. (Before you flame me, the keyword there is "properly", just in case you missed it.) The BSDs come close, and I could probably do the same with them, but I personally prefer Slackware (probably because I've been using it as my own desktop since late 1993 or thereabouts).
THAT is why. It's been over a third of a century since I started making money with computers & networking, and I'm more than ready for my "tech support for end-users" hat to go away. Linux has a shot at doing just that. Will it happen to any extent world-wide? I honestly don't know. But in my microcosm it is happening now, one machine at a time.