This question has been inspired by the fact that I’ve recently heard the Swiss talk among each other and I started to dig deeper. Having done minors in Italian and American studies which each included different depths of linguistics, I found it fascinating how I couldn’t make out a single word while speaking German.
Then I learned Swiss German (Allemanic) and Standard German differ substantially — the former doesn't have all the cases like dative, accusative, nominative and genitive, but only two; it has different suffixes; word orders and of course a lot of loan words well integrated in its vocabulary and some mutually unrecognizable variations of common words among other specificities.
I read more, but I couldn’t find an answer as to why Swiss German is classified as a dialect as opposed to a whole different language. A Slovak will understand a Czech and vice-versa — they are still different languages. Same is true for Serbian and Croatian, but in turn, they are considered one language: Serbo-Croatian.*
Conversely, I found the following anecdotal evidence in comments about the topic to support that Swiss German is, in fact, it’s own language:
“I'm Swiss myself but I had a similar experience once. I was using a public bathroom and overheard a conversation between two women. I couldn't understand what they were saying and I didn't recognize the language at all. Until it suddenly dawned on me that they were speaking Swiss German. I'm from one end of the country and they were from the other. it took me several minutes to realize that they weren't speaking in a foreign language and I still didn't manage to understand half of what they were saying.“
Furthermore, the following even more extreme example:
“In the RS (military bootcamp) we had on[e] guy from [G]risons and one from [V]alais that couldn't understand eachother (sic!) at all. Some of us from cantons inbetween (sic!) had to translate for them [as they each were talking their own Swiss German dialects].”
A native speaker of Standard German will not understand a Swiss speaking Allemanic; and a Swiss German would not understand Standard German if Swiss Standard German would not be taught and used in formal education and in the limited written settings as it is. Television, ads, news papers, even politicians in the federal congress will speak Swiss German and will only use (Swiss) Standard German for keeping records and the laws, regulation and executive actions are probably set forth in the Swiss Standard German (the formalized standard as accepted in Switzerland which may slightly differ from Standard German in Germany).
I see the cultural and/or political motivation for the non-claiming of these two languages, but I don’t see a philosophical or linguistic reason for it; accordingly, is there such a reason or how could it be argued?