Well even if guess some kind of response is needed for SBS to know why people are not joining I’m not sure if this would help SBS to change something to let more people stay.
Point one you address: the same persons are responding
Well…what to do about it. Block the possibility to respond to other player’s threads once you reach 200 posts? Joking aside it is just natural that you will read some names more often than others. To change that we would need more knowing people on the forum to answer questions because if a question is sufficiently answered it is less likely that someone else will answer the question again and if the pool of answering players is raising the recall value of name will decrease.
Point two you address: you have seen a locked thread
Instead of locking a thread they could delete/hide it but this would be even worse. But keeping a thread open could be also worse…e.g. if the original post was about what package you need to participate in beta and after a while people are starting to talk about what they will do once beta starts…but it will not help others having the same question to read dozens of pages about unrelated stuff. As far as I know the mods are always adding a post why they are closing the thread and this seems to be the best compromise. If you have a better suggestion I guess they could change their mode of operation.
And just to mention it...not getting involved is totally OK if you got the impression this is not your game. But if it's really just the forum you don't like I would suggest too that you should return in some months if there are some more information available.