I'll preface this with a disclaimer that this is pure speculation on my part. I have no knowledge of any facts on what has happened here, I'm just going from memory with what happened at my previous job.

About 7 or 8 years ago ALPA operated their own web boards for each property. You could even set it to send you emails of posts made, and you could post from your email. They were sued, or threatened to be sued, by UAL. The claim I believe was that the boards were inciting and promoting illegal job actions. ALPA's initial response was to shut off the email function, to force everyone to come "in-house", so to speak, to utilize the board. At some point I guess they realized even that was too much of a potential liability and shut the boards down altogether.

If this is true with the Spirit Board, I'm not saying its right or wrong, but an argument could be made that a board that had ALPA logos on it, contains specific LEC forums, and has reps posting meeting notices and minutes, is posing as an official ALPA sponsored board, and opens them to similar liability that ALPA national wasn't willing to risk. Shutting down what most saw as a SPA ALPA bashing site was likely the motivating factor for whoever brought it to national's attention, but I'd guess it was only icing on the cake for national, second to limiting their liability.