The distribution you are talking about is Debian and the "nonfree" tab is in
the "Synaptic package manager".
But why is that the people haven't left their proprietary OS behind?
Mainstream user uses what is practical, cool looking and stable.
Mainstream users use what comes with the computer. They were offered no other
option (not even the option to not have any operating system). And many
believe that the operating system comes gratis with the computer.
Product tying is forbidden. If the law would be properly applied, users would
have to pay on top of the price of the computer to have an operating system
installed. Many users would realize the existence of that price. Nowadays, it
actually is a significant part of the total price of the lower-end computers.
Vendors would certainly start proposing GNU/Linux as a cheaper option.
Sure Microsoft and Apple may then drop the price of their operating systems
to 0... and abuse their users more in compensation. But then, users would
hopefully start to realize they are abused and, for this reason, get
interested in the free operating systems the vendor would propose.
Anyway, I am all in favor of material that explains the philosophy of the
free software movement, of killer-apps, etc. All that is good. But the main
obstacle is product tying, imho.