Like with most things, it's friends, relatives and professional requirements.

When you need to do work for school or the Office from home, you more or less need to have the same programs. And even if there are alternatives, you most likely don't feel like learning how to use a different program for the same purpose all over again.

Also people still like to ask friends or relatives about their problems. When you don't already have a sophisticated Linux user in your circle, you are unlikely to even get the idea of using linux.

Also nowdays for the youth, more and more activites are online, also like gaming. It's not just about the gaming, but also about doing something with your friends(online). The proprietary Software used here is a stronger limiting factor here.

I would recommend an easy Linux Distro to my mother, since she doesn't use her computer much unless to browse, edit and print documents(which will be shared in printed form)

My father, while more techsavy, couldn't use Linux, due to all the proprietary software he is using professionally. Also since he allready knows his way around Windows, the differences would upset him. He wouldn't have enough patience to learn the different environment.

In conclusion, it's much easier to recommend (and get the person to learn it) Linux to an unsophisticated Computer user, rather than someone who already is used to handling his current OS. So at the root modern Schools, who often provide Windows and only Windows for free, are to blame for noone really using Linux.