interesting you think all of these are made by school’s admin? It doesn’t seem that way for most, though I have seen admin-run ones. e.g CHCH has it on their main page: https://www.instagram.com/chchschool/
Many have poor graphic design, weird logos and don’t even follow the school’s main pages. It is abundantly clear for my own prep school, the acceptances page is NOT run by the school unless they are proactively strategizing to make it seem student run, which would be very bizarre thing.