One theory that we had is that people would submit melodies that they were the most famoliar with -- childhood songs, top hits, melodies from their favourite video games. And this ended up happening! For example, here is a Romanian childhood melody or the Family Mart jingle from Japan!
Below are the melodies in each country's top 2000 that were not seen in any other country's top. The size of the rectangles indicates the number of total harmonizations for a melody -- bigger rectangles mean more popular melodies. We'd love to tag more of these, so if you know any of them, please let us know!