It's not that they're blissfully unaware. It's being thaught in school and almost all official writing is done in the so called 'written German'. But it's simply not the language you speak (safe for a reason to the contrary, like not everybody understanding it). Even in written (private) communication it's used quite a lot, like in mails, sms, ...

Oh, and at least for Swiss German: It is kinda a different language (but extremely related to the written German): It's not just an accent with some funny words, but has a slightly different grammar, too. Most glarious is the lack of most of the verb tenses in Swiss German. So pupils have to learn quite some stuff to be really fluent in written German.

And even just within Switzerland there are dialects I don't understand (as in no clue what they're talking about). People speaking these usually switch to a more conformistic pronounciation when talking to people from other areas and don't use some of the more obscure words.

And for the reasons this all exists (at least for Switzerland): It's cultivated and all kinda part of your local/national identity. Politicians who speak a "too good" written German are deemed suspicious, almost all of the local culture (theater, local movies, even most of the Swiss tv produciton ...) is in Swiss German.

[Native Swiss German speaker, here.]