Participation Grade Rant

I don't understand some participation grades. I just got graded for HILD 7A and got an 18.9 out of 21.

I attended every single discussion class, answered questions aloud in every single discussion class, and did every assignment. Why are my points being docked? It's so arbitrary. We even filled out a Google Form that self-reported how much we participated and I indicated all those things. What else could I have possibly done to get full credit? I feel like this is so frustrating.

Update: Emailed TA who said that meeting class requirements only gets you a B. To get anything above that you have to do "exceptional work." So essentially, it doesn't matter if you do what the class requires you to do. You have to do more. Insane policy. I guess doing what the class tells you to do isn't enough anymore. You gotta pull yourself up by your bootstraps and be exceptional in every single class you ever take or your GPA will suffer.