Most of those points don't hold water.
Take 1,3 and 6 all covering the same point, 1. some have moved on. 3. same statement busier, moving on. 6. again moving on.
While members move on according to the bottom of the opening page we have New Members, everyday or almost there is a new member signing up, sometimes two. The forum is being replenished daily so that would be more than enough for those lost.
5. KK KL bickering! really, that would put people off? Look at the sister sites there is more arguing and bickering going on in their equivalents to 'Off Topic' threads. Secondly look at Australian craft brewers, there is no bickering whatsoever on that forum. And since the moderators, both involved with Australian Craft Brewers started running this forum deleting posts and removing threads this forum has ended up the same. Both are as dull as dishwater. That is what makes people leave.
2 Facebook has always been there, so where do those who are not on Facebook go who aren't on here. There are plenty of brewing forums doing really well, why? They don't get posts removed and threads locked. Grmblz mentioned sterile I agree.
When Austin sold his forums to Keith they were a viable proposition AHB at the time would generally come up first on the search engines it was informative and busy. So what went wrong, not the exodus. AHB was becoming just as busy while Australian Craft Brewers was flagging. I don't have to point out what happened I think most members know, they tried to fix something that wasn't broken. If Keith tried to sell this forum today he wouldn't get a brass razoo for it. A forum needs to be busy have members willing to pay to be a member and sponsors, which is another thing they have lost. I wouldn't be surprised that the only paying sponsors are Keg Land, Brewman and Inkbird.
As an aside here is a book well worth a read, 'The clowns are in charge of the circus' Kenneth A Scott.