The rule against replying to old threads is the dumbest forum rule ever
I'm not talking about MovieChat, which has no such rule, but a lot of forums do. And there are also a lot of forums that have an "unwritten rule" against it.
How did such a nonsensical and irrational rule become so widespread? The people who make and support this rule are mentally ill, specifically, they have a phobia (irrational fear of / aversion to encountering new replies to old threads).
It's not really the dumbest forum rule ever, but it's the dumbest common forum rule. I know of even dumber ones that are uncommon or unique to one particular forum, such as Doom9's rule against asking, "What's the best...?" They "justify" that rule by saying that "best" is subjective, which isn't always true, and even in cases where it is true, arguments over "best" tend to be especially good at producing useful information, regardless of whether or not anyone manages to conclusively prove that something is the best.