Various forums automatically do this to new members or those who’ve not posted to a certain threshold. That’s because they’re trying to avoid spammers. Sometimes, some forums enact this when they’re seeing a rise in spam.
I’ve not encountered that msg myself on THS, though, except maybe when I was new.
On THS, they award badges, some of which allow increasing latitude with what the individual can update or such, sort of like a lightweight form of moderating.
More info about the software: Censorship! - #18 by Carla_C