Or do most people lack the cognitive ability to use more than one OS, and need crappy 'Microsoft Essentials' classes to teach them anything beyond how to game and access their Facebook accounts?
They lack the interest the same way someone who learns driving an automatic usually has little interest in learning to drive a stick-shift (actually, here in Spain there are very few automatic transmission cars so everyone needs to know about the stick-shift, but I digress).
I deal with last-year undergraduates who still don't know about Word styles, who still write the content tables by hand (because they don't know about the possibility of using the title styles in their Word documents). Believe me, they don't care to investigate in most cases.
Actually, most of them still will put text walls in their Powerpoint presentations so they can read them. And yes, they usually had classes about it in high school. But they didn't care.