I've been on the forums since 2019 and I can't recall a time when promotional threads didn't just devolve link dropping threads. It's always kind of been like this. The mods tried to put up a promotional mega thread to circumvent the problem and pinned it to the top of the forum. Unfortunately, people would still make new promotional threads anyway, and I think at some point the thread was unpinned.
It's hard to say something is rude when it's true. When I first got on here, I tried my hand at promotion a little bit. Didn't want to be too spammy or seem too desperate. But in doing that, you're overtaken by the noise of other creators who are, to put it nicely, less self-aware.
And, nothing against anyone else here, but I'm pretty against sub4sub threads. Past getting your first 15 subs, it doesn't really help your metrics. It can actually hurt in the long run since, apparently, having a lot of dead subs can result in worse placement in the algorhythm. Though, with the way technology works, that could have changed by now. Also, I just think sub4subs are annoying.