I don't think that every forum is dead and it really depends on the topics, niche, interest levels. There are many forums that are busier, but I agree that people just don't post topics or reply like they used to. The people that visit this and other ATV forums are usually looking for something, people aren't "sharing" like they did because they are doing it elsewhere such as facebook and twitter.
However, there are still so many visitors to this site that read and such but never login or are encouraged enough to reply or start a topic. Mobile has affected things but this site and most current sites all render well on mobile screens. I just think its a facebook/twitter world where people are used to getting notifications on their handset and unless someone gets a notification or an email that doesn't land in spam, they don't get drawn back.