In addition, some of these do not have a large social media component so let’s say that the SDMB is the 500th biggest social media platform in the world (which is sort of weird to think about but whatever.)
It’s well known that the Russians have at least a minimal social media disinformation team. Let’s say it’s 10 people. If I were them, I’d task 5 of them to fully dedicate to the top 10 sites. The other 5 could try to drive by on all the other ones. It isn’t inconceivable that a drive by poster could hit at least 5 message boards a day, if not more, given an 8 hour day, 2 days a week off, and having to jump through verification processes. At 100 sites apiece it would only take 20 days to hit them all. Even if you assume that they’ll hit some of the lower ranked sites as well, and also spend more time on the top 100 sites than they do at the SDMB, it is still utterly conceivable that they could hit the SDMB in 100 days.
Not to mention the aforementioned hypothesis that some of them are simply dedicated disinformation partisans or even professionals who do this in their off hours as a busman’s holiday.