So, why isn't this a thing yet?

[Canadane]

Forums ought to have some sort of cutoff. Like 'if the last post in this thread is from more than 90 days ago you cannot post in it.'

That would be miserable. Old problems never solved can’t have solutions posted in. Old topics of discussion are never truly outdated, they don’t need to be cut off.
It’s much better to bring up old topics like this than create new ones, which would only hinder people searching for help.