I'll admit that I'm not that updated on recent changes but reddit used to be open about the vote counts being intentionally inaccurate. I believe this at a point started to include scaling the vote count so that the average popular post would have 10-20k or so up votes, even if the actual vote count would be much higher.
So this would make it almost impossible to make any meaningful conclusions from vote count / active users alone.
That's obviously a subreddit local rule and as the message said doesn't target dedicerad instances, but social media links in general. I dunno why they do this but it's a pretty uncommon rule I think