That said, Disney has spent years now cultivating the FB and Twitter crowds at the expense of sites such as this one. Look at my old online 'home' LP.com or Micechat and watch the tumbleweeds pass to see how once vibrant communities have lost their voices because of these social networking sites
I don't see the social networking as a reason for the decline in those sites EXCEPT in the aspect of 'stale technology'. Sites like LP.com were dinosaurs and the format just isn't tolerated by the next wave of users. vBulletin grew long in the teeth and didn't have the capabilities like great mobile apps, live notifications, etc that the new alternatives like twitter, FB, etc have. So the new alternatives had a technical edge that offered attractive things. That put the 'old' sites behind the eightball as the next wave of users came into being (every site has 'generations' of users that start and die...)
LP especially was antiquated... Micechat took the plunge with vB4.0, a move wdwmagic WISELY declined and instead pivoted with great success. Micechat has yet to abandon that dead duck... but I wonder if they care as much anymore because (IMO) the discussion forums really aren't their main focus anymore. They put all their chips on becoming this home of web articles instead of an online community. They put all their promotion and leads into their Wordpress site. They don't even post that their articles are available in the forums anymore! The core group RARELY posts in the forums. Everything for them now is the blog articles and comments. They've basically changed their focus to becoming a site... much more like a insidethemagic. Trying to create a steady stream of content to attract EYEBALLS and less concerned with building a community.
The other reason these people retreat to places like twitter, etc is because they don't have to operate under scrutiny of a site owner or mods, they don't have to face critics of their content, they can basically blow their horn as much as they want and selectively decide what responses they want to listen to. It promotes the building of cliques and selective acknowledgement.
So what I'm trying to say is... I don't agree with your theory that social media (and Disney's engagement) is necessarily behind the demise of those classic communities... but more about missing the necessity of keeping current with user's expectations of technology holding them back, pivots in focus, and the 'freedom' from oversight that the new platforms give people.
Think about how big these twitter circles you are focusing on really are... a few dozen people each? Sure there are multiple circles of people that overlap.. but they really don't converge into one single community. Contrast that with something like Micechat who at their peak could pull 100+ people together for a MICECHAT thing.. not even specifically Disney. Disney twits are just people who all use twitter to talk about Disney... they aren't a online community like Micechat, LP, or wdwmagic.
For micechat in particular (IMO).. the idea of a 'popular website with news' verse 'a popular hangout to share ideas and conversation' was a business decision they will look back on years from now and realize that was the turning point. Not when they had to acknowledge Al was no longer a factor.. but when they abandoned being a social exchange and instead tried to be a content provider.
Again, many of the Tweeters out there once were active here, but have chosen the 'safety' of the Twitverse over open communication here.
That's a huge part of it... they feel they are in control vs playing in someone else's house.
