[ssivark]

Math has a culture where author affiliations are often mentioned only as a footnote, at the end of the paper, and not at the front of the paper. For a field with such culture, where it has repeatedly been shown that quality work can come from many places, this kind of coarse gatekeeping creates a very unpleasant environment. I'm trying to imagine the motivation of the platform creators, but drawing a blank. Maybe it's a ham-handed attempt at spam filtering.

[gh02t]

Their about page says that they use an algorithm to verify if you are a PhD candidate in math/stat. I don't really think that is a good requirement for the exact reasons you say, but I would guess it's set up like that to make this automatic verification more practical.