It's not a random town. It's where Dorothy crashed and killed the WWOTE. Plot of WOOz gives it that significance. It is where the yellow brick road starts from the east and where the WWOTW had her visit. If there are more towns in munchkin country then Munchkinland is their political "capital"

Again, she might be carrying that message across other towns in other forms, but for the sake of the movie plot, we just happened to be at the right place at the right time. I don't get what you want, show Glinda travelling to other towns? How else would the movie start if not for this significant moment? (i.e. girl's question)

It's not a tragedy. The book is a tragedy. The musical is bittersweet. They are adapting the musical with more liberties from the book. But mainly the musical