It's a shame, really. Linux is soooo much easier to install and configure on Intel machines these days; MUCH easier than the days of Red Hat and Mandrake. It takes just a little bit of education and research, but due to these days of convenience, instant gratification, and "Woo... new shiny!", many just aren't willing to undertake the minor bit of work needed to migrate to Linux and would rather just buy new machines. This is one point where I'm in total agreement with zen over at PowerPC Liberation, although I'm not as blunt as he is about it
Misinformation and FUD play a part as well. I hear a lot of, "I don't want to spend time constantly configuring and tweaking my system", which really isn't needed much with certain friendly distros. For instance, I'm running Ubuntu 16.04 on my 2008 white Macbook, and other than some theming, I haven't really done any tweaking to the system, as I haven't had to do so. My Blackbook is going to get Debian running Openbox, and that machine WILL be tweaked and configured to death, but that's by my choice as I enjoy doing that (and making it a zippy system, using what I learned from my PowerPC installs).
It still takes a minor bit of research and work, but I think anyone could take one of the easier, more friendly distros and run with it.