It didn’t used to be like this. Using an OS used to be hard work. When things went wrong you had to dive in and get dirty to fix things. You learned about file systems and registry settings and drivers for your hardware. Not any more.
In other words, people used to be technically literate because they had to be. Now, it's possible to utilize technology without knowing how it works. Think for a moment about what that means.
This sounds very much like a case of a species evolving to meet its own (lack of) need. People aren't tech literate because you don't need to be tech literate to check your email on an iPad, just like I'm not very proficient in spear hunting because being able to hunt a wild animal is no longer necessary to feed myself.
Not everyone needs to be good at everything, and mastering skills has an opportunity cost. Yes, it would be nice if every teenager could spend the hours required to know how to install Linux and work around the Linux desktop environment, but how many hours would that take them? Every hour that they spend learning how to install and use Linux is one hour less that they have to spend on guitar lessons, or learning a foreign language, or automotive repair, or oratory practice, or whatever other pursuits they might choose to invest themselves in.