More likely that terms that are continuously mentioned in huge numbers (and therefore don't count as "trending") are omitted.

There are more principled ways to do that than a blacklist, though, like looking at current frequency compared to typical frequency. That way even something commonly mentioned could still genuinely be trending if it gets mentioned much more than usual on a particular day.

(It's possible there are scale-related reasons that make this infeasible, though.)

Just not tracking the frequency of the most common words that will never be in the trending topics is probably a big performance win. I'm sure there is an additional blacklist that includes stuff like "and" and "the".

You know you've made it when your brand name is a stopword.

No, it just prevents comment from trending. Not just disparaging comments, all comments, it seems.