Pretty sure the whole Allo Class Threads subsection has only been open for about a year or so, so I don't know where the "past years" idea comes from.
Either way, what the hell does it matter? Some of the more active threads on that forum are from classes that are not in the incoming class and it serves the useful function of allowing classmates at schools that do not set up classwide websites to chat with each other and to serve as a resource for those in lower classes at their school. If your gripe is about it being harder to find the current year thread for whatever school you're admitted to, check out that handy "Search" icon at the top of your screen.
So yeah, not so much in support of this proposed overregulation. Take it back to pre-allo.