>>1273531It's not hard to figure out. The board has a limit of 10 threads per page (or around there). So a total of 150 threads can exist at one time. Thread #150 will stay alive so long as a new one isn't made. But when it becomes #151 it's gone.
Threads used to die in the order they were created, regardless of page location or activity (/f/ follows this rule). Now they'll stay until they go past page 15. The only way that happens is no bumps. This is facilitated by their being a bump limit of 250 or so. After that no posts will bump it.
Make sense?