Oh, I get what you're saying, OP.  It took me a minute to figure it out--there have been fewer accusations of trolling in the past 3 years, based on the use of the word "troll", right?

That might be because Lauda, TECSHARE, Vod, and some others have left the forum (though those members left more recently than 2019).  I think I recall Lauda in particular using "troll" a lot, and TECSHARE as well.  I'm not sure your data reflect anything more than that, but it is interesting nonetheless.

I'd be more interested to see the change in the usage of the term "shitpost" or "shitposter" since 2017.  I'd bet it's decreased somewhat.