I don't know what OP is going on about with the threads on /b/.

if a thread is marked for deletion then if you're gonna post in it, no one is gonna see it, as it should be ┐(ﾟ～ﾟ)┌

everything on the first 10 pages (the old page limit) is within 20 days old, and if you're seeing a lack of new threads, that's because you're not posting them (since you can't bump old threads)
you rarely saw threads fall off the bottom before without being marked for deletion, so it's not like anything has changed there ヽ(ﾟρﾟ)ノ