Mathematics is by far the most accessible "science" in academia. Anyone can, in theory, produce novel results with nothing more than a pencil and paper. And while the existing literature may not always be readily "accessible" (in the easy-to-understand sense) it is pretty widely available (often online and certainly via any decent academic library).
But "frontier" mathematics is still a highly advanced, highly specialized field. It can take years of study to be prepared to understand the established theory and results for a given subtopic.
These two observations, taken together, lead to the predictable outcome of a lot of math "enthusiasts" with an incomplete understanding of the field loudly asserting that they have discovered a radical new result. Often they lack the foundation to even understand what they are doing wrong.
The reluctance of mathematicians to engage with amateurs that come off as cranks is a symptom of how accessible the field is.