It's no surprise really. We're at the end of a 5 year cycle or so and we are experiencing a changing of the guard. I would say the difference between now and the last couple times this happened is that anime is definitely on a downturn in the USA. Heck in general you could argue. The AMV scene is not the only place hurting just look at the fansub scene (and please let's not debate warez or what-not about fansubs). The fansub scene even a couple years ago was ripe with a lot or large groups and multiple translators. Now it's a bunch of splinter groups featuring a handful of the same people translating (and the rest of the "groups" are just remuxing crunchy subs or ripping DVDs). Why do I mention this? I think in recent years there has been a shift in the fansubs scene to the point that a large amount of the groups no longer even care about the anime itself. There are quite a few well known groups that engage in more 4chan-esque behavior and talk about subbing and trolling as one and the same. These are not hardcore anime fans like we had in the early 00s who did digi-subbbing and their motives are quite different from the early 00 groups who were also different from the 90s groups.
A similar demographic issue happens with AMVs. This site and its community is a more hardcore venture for the average type of anime fan that exists today. You need a pretty strong interest in anime or AMVs to care about coming here and you actually need to dedicate some time to be involved or noticed by the community. Contrast that with the throwaway status of AMVs or anime on a place like youtube or random internet forums. Anime does not have the same status it once had and this site and its community is most certainly not built to attract or foster someone who doesn't really care much about AMVs/anime. That leaves us with potential new members as: 1) someone who experience making AMVs and is pretty hardcore about it or 2) big amv enthusiast (but they no longer need a source like the org because the content they desire to see may already be posted or discussed on numerous anime blogs).
To be honest the site's lasting power has impressed me but that's because there is a strong core social community in the mix that sustains it. I think the core of this site currently has two major groups. Active AMV creators and the forum/#amv social community. What happens when these 2 groups no longer intersect?
Caveat
You are reading the post of someone who considered the org a step down from its small insular AMV ML roots at the time it went live.
Bonus
http://www.animemusicvideos.org/forum/v ... 97#p854797