His answer was quite simple: because Linux is not shipped preinstalled with most sold computers.
So, why do the laptop vendors not pre-install Linux (or FreeBSD or something else)?
There are two reasons: Push and pull. First, pre-installing Windows is relatively easy for them. Microsoft has a gigantic department that supports hardware vendors, handles licensing, works with them to customize and tune, and builds its distribution (install, configure, support) mechanisms around the needs of those OEMs. In the Linux world, such a thing just doesn't exist. RedHat had a little bit of it, but it never went much of anywhere, and now that RedHat is being absorbed into IBM (who no longer sells computers to individuals, neither desktops nor laptops), that need won't be seen. And other Linux packaging companies are even smaller. So let's go one step further: Why does Microsoft do this, and "Linux" does not? Because Microsoft is customer and user focused. Microsoft knows who buys their products, in the case of OS licenses mostly OEMs, and it is willing to help its customers make that an easy and profitable experience. Microsoft knows who its end users are (in the case of Windows, the humans who push buttons and move mouses, not the OEMs), and it tries to create a product focused on the needs and wants of those humans. In contrast, Linux is run by engineering and computer science types, for whom the beauty and elegance of a line of kernel code, or the coding style of a DE, is much more important than whether it is easy to install and support, or whether users actually like using it. So Microsoft pushes windows.
Now on the pull side: Windows has an extremely large market share of the desktop/laptop market, whether you like that or not. That means that for users of computers, choosing Windows is a pretty easy and safe choice: the skills are there, creating a support infrastructure is easy, it is relatively risk free. So users want Windows, and vendors are happy to oblige.
It also means that people who write software (applications) need to first and foremost support Windows (which gets them about 90% of the market), then Macintosh (which gets them to about 99%), and only after that they need to worry about the Unixes. And many software vendors stop after the first or second step. I have so many examples of minor software products that only support Windows. Not because the makers are evil and hate FreeBSD, but because of very simple economics. Often (perhaps even typically), those are commercial products that are not in-and-of themselves profitable, but are needed to support other products, for example hardware configuration tools. Current examples for which one needs to use a Windows machine in our household or with neighbors: The monitoring tools for Omega industrial controllers, the setup tool for UPB remote-controllable light switches, and a software package our neighbor uses for tuning his ECU (engine control unit) on a modified Corvette via the OBD2 port. All these are small software projects, not distributed to millions of customers, and created by "small" companies (much smaller than IBM/Microsoft/Google) that don't specialize in software, but have to do a little software to support their real products. For them, Windows makes perfect sense: it gets you a very large market penetration for just one investment. The RoI on supporting Mac is small by comparison.
Classic example of Network effect. Esther Dyson put it really well: Microsoft won the election for preferred desktop software perfectly fairly. Unfortunately, our system does not allow for a second election.
