It's a discussion forum. Arguments are inevitable. People disagree. Egos come into play. Grudges.... bad feelings.... but also I think it's because this community is small, there are only so many people participating, and there isn't enough other people to square off with. It's like a large family that sees each other often and people hold onto arguments. One cousin fighting with another cousin because he stole his girl 10 years ago.
But I think the decline in users is from the slow decay of this medium. Young people don't use forums anymore. They use facebook and snapchat and Reddit. I find that most of the people who post on Reddit are younger. Most of the people on this forum are older. It would be interesting to do a poll to get an idea of age demographics.
I also think there's a distinction between people that view this forum and people that participate. During the season we could have 100+ people viewing a thread, but how many actually post? 10? 20? Why do you think that is?