That's not really fair for you to say when you've not been part of a gang.
Each gang was a small group of friends - or even a family. Their private forums were for private discussions, not the sort of thing that they would post in General Discussion for anyone to see and for n00bs to reply to.
If you look at the quality of many of the posts in GD or the other general subforums, you'll know why people prefer to interact with their friends, not the random crappy people that clog up the internet.
it also led to the downfall of the forums as well since thats all we ever posted in and just ignored every other part of the forum