With respect, I've heard the whole "goes in cycles" thing before and I'm not sure that's what this is. These forums have been in decline for well over 2 years now with no real sign of picking up. Heck, there are sub forums on here that haven't been posted in for 2-3 years (like the Pressure point forum).

Other MA site forums at the moment are positively thriving.

I can't tell you why that is happening, but I think there is more to it than being cyclical. I think one reason is that there are lot more specialist forums now online than before. Really good forums dealing with specific arts. So say a person is only interested in Aikido, Chinese Internal Arts or BJJ, there are really good forums for these subjects.

So I guess part of the reason for the decline on FA forums is increased competition from other MA forums.
"Let your food be your medicine, and your medicine be your food" Hippocrates.