How shall we know what you know?
German is a language that, apart from standard German, has a large number of dialects. So, apart from Swiss German, there are many more dialects. Swiss German itself again has a large number of sub-dialects. Basle German is different from Appenzell German or Berne German. There are dialects in Germany and Austria that have similarities with Swiss German. All these dialects are called Alemannic German. You can find a Wikipedia article about it.
I can't answer your question *why* it is different.
However, if you can answer why Cantonese is so different from Hunan dialect of Chinese, then I guess you have answered your own question.
Oh, but I missed the original point.
All reginal dialects of German are very different from Standard German. The original local language in the north of the rebublic of G. is so different that they are officially (scientifically) considered different languages; I don't know in how many other regions this is true, as well.
The official language of Switzerland is High German, not a Swiss dialect based language form ("High German" is often used as a synonym for Standard German, although it means technically a slightly different thing).
But Swiss people normally speak their regional variations. Except for the times when they meet someone who can't understand it. That's exactly what Standard German is for...
In a survey from 2006, 70% of Swiss people said that they feel like High German was a foreign language to Switzerland and Swiss people. But only 30% said that it was a foreign language to themselves.
As long as you read and write on the net (in German), you would have trouble to say from what country people come from. Everyone writes Standard German ;)
*Disclaimer: All of this is mostly written from memory.
You should maybe also know that Standard German is an artificial invention. Originally, there were only these many, many dialects, and therefore, communication was pretty hard when people travelled or read texts from other regions.
So, Standard German was invented so that we had a language that everyone would understand.
This is not just one of the dialects that has "won".
It
started when someone wrote a text that was veeeeery successful, so everyone had
to learn to read this language version. It was the first widely spread
translation of the Bible in German. He was using a language mix that mostly
came from the center and south.
The spoken version of Standard
German evolved when people learned to speak this Bible text like a
foreign language. They based their pronounciation of the words strongly
on the script, since most of them did not have any speakers to hear it
from. But their way of pronouncing the words was influenced by their
language, of course.
People really liked the way that the northern people were pronouncing the words. It was so close to the letters that it seemed quite "refined" (although it was very different from how the center and south would have said things), and so this way of speaking German was one day used as the basis for Standard German.
So you can say that Standard German is not at home ANYWHERE in the German speaking lands.
In northern Germany, the regional dialects have started to fade (because they had a bad reputation for a long time. They said it was a language for uneducated people.) Standard German has turned into a living language there.
But it's a must have for writing books and making television, for everyone :)
There
are different (but very similar!) standard versions for German for the
republic of G., Switzerland and Austria today. Of course, since it's the
governments who made the rules.
Swiss French (Patois) is a Franco-Provencal language, which was formerly spoken throughout the Romandy (except in the Jura). Today the Patois in Switzerland has been practically completely displaced by the French and is spoken only by a small minority in the Valais as mother tongue. More recently, efforts have been made to save the Patois from extinction.
French speakers (Parisian French) look down at Patois speaking people. I mean really extremely scornful. In German the dialect is not despised.