So Chevy Chase, the actor who plays Pierce, was a very problematic person on set, especially during these seasons. Most of his colleagues described him as racist and difficult to work with, and he was also very jealous of Donal Glover's talent and the attention he was getting and would attack him with racist slurs/verbiage, which Donald himself confirmed in the humblest way. He even had issues with the creator so his screen time was drastically reduced, as you've noticed.