Austrian accents

I just binged watch the entire first season and was really surprised to see such a difference in German and Austrian accents. I speak fluent German but was challenged by the Austrian dialect. It reminded me of the Swiss German my father used to speak, and some of it was entirely indecipherable lol. Good thing for subtitles. Why is there such a difference in the two languages when I keep getting told both countries speak so called "hoch Deutsch"?