I've noticed this too and tend to agree with your observation, but I don't think this is necessarily because certain people don't get or are not naturally talen

I've noticed this too and tend to agree with your observation, but I don't think this is necessarily because certain people don't get or are not naturally talented in a specific subarea of mathematics. My math professors told me that math majors tend to fall in love with the second upper-division math course that they take, because in the first one, you're still struggling with the details of moving from mostly computational to proof-based problems. Usually this first course is either real analysis or abstract algebra, and since all analysis and algebra classes tend to build on the fundamentals of these courses, this may show up in the subsequent classes that you take within these fields.