It's very common for forums to have rules against posting in a thread that hasn't seen any activity for an arbitrary amount of time. When you do that, you will often cause a thread that has fallen from the front page to bump back to the top of the front page. It's not clear why this is a problem, though. Maybe regulars just dislike seeing old topics brought back up?

Post in a old thread, and often mods will immediately yell at you and close the thread for having committed the crime of necroposting. Which only makes visible the old post for the minuscule but devoted part of the userbase that actually waits in the "thread by last post, chronological order view". Those people by definition, want new stuff and are annoyed by the old thread messing up the feng shui of their post order. Probably an OCD thing.

This is mostly because those old forum software lack a "thread by creation date, chronological view".

So they close those discussions that happen on the timescale of years. They close the discussion that are google's top links. Then they get bored waiting for new and leave for discord. Where nothing is recorded nor searchable. So all this effort and knowledge goes right down the drain.