The trope has always sounded to me like \\\"there\\\'s only a Jewish character here because the producers, director, etc.\\\" are Jews- it smacks of the whole \\\"Jews control the media\\\" idea.
Also, it\\\'s not like Jewish characters are \\\"out of place\\\" in any work not set in New York, California, or Israel. I\\\'m sure that there are Jewish populations in every state in the United States, and I know that England has a Jewish population as well, and my contention is that in the far majority of works, there\\\'s nothing odd about having a Jewish character, because Jews are often middle class and educated, as are lots of characters in tv and movies.
Regarding the South Dakota example,that reminded me that I just added an example of this trope to \\\'\\\'ParksAndRecreation\\\'\\\', where it\\\'s noted that a minor character changed their name to a Jewish one, as Jews are exotic in the small town Iowa setting. I was thinking though whether the trope would also say that it\\\'s \\\"wrong\\\" that a character mentions learning a Yiddish word from \\\"David Meyers, the Jewish guy who works at City Hall\\\". I think that the trope would, and I disagree.
Yes, it\\\'s possible that this line got there because the cast and creators were Jews/knew Jews, but I don\\\'t see what\\\'s so unbelievable about the idea that the town has at least one Jewish resident- because there are Jews living in Iowa.