People see that the Celtics are struggling, so they have something to say about it. When things are going fine, or there's no chance of something changing, there's little interest in giving input.
Not many people enjoy discussing the relative merits of specific lineups and exact minutes for different players (like us). Throw out a rumor that a major guy might be traded, however, along with some epic failures in the past couple of months, and you get lots of chatter.