I have no idea how/why things evolved this way. Maybe an email to the curators might get a response. They might be flattered that someone asked.
I can see where the commercial side would end up this way. If you target your advertizing to people getting married, then you become a wedding photographer. If you do product photography of jewelry, then you're a product photographer. If you spend 30 weekends per year shooting weddings, you might not enough energy left to do anything else, and the people you hang around with probably do similar work, so pretty soon, even if you didn't intend it, you're in a silo.