I know. However, there's nothing Dutch about it. Furthermore, how did a mispronunciation turn into windmills and tulips? Let me guess -- money and the negative PR re: Germany.
Maybe
Plus back when the Amish were coming to America there was no unified German State but a collection of kingdoms (until 1871).
Many of the Pennsylvania Dutch aren't even technically 'German' because they came from areas in Switzerland, Austria, the Czech Republic, the Netherlands, and Germany. They just predominantly spoke German which drove the name.
A lot of them migrated to Rotterdam, Netherlands which is where they left to go to the USA.