What you said is that people moved onto other sites because they couldn't bear the censorship. So, what other sites? I'd like to know.
Or are you saying that they've moved onto sites on completely unrelated topics and given up on home theater, essentially taking their ball and going home?
Maybe that's the case, but what I think you're forgetting is that most people aren't belligerent jerks who need to be moderated (or "censored"). Not everyone, but most people can carry on a conversation without launching into abusive personal attacks. The ones who can't behave themselves, and may have fled for other pastures, are fairly few in number - though of course they do tend to be the most vocal and prolific of posters, so their absense may be felt more than others'.
In any case, I have to side with the apathy explanation. Outside of forums like this, I don't know many people in real life who give a flying crap about home theater. Some may own Blu-ray players, but relatively few movies. They just aren't passionate about things like this.