Well, I know from their direct statements that a number of my ex-squad mates (and a notable nemesis or two) left because of the new version not agreeing with their hardware--and their own set-in-stone ways.   AH3 is a much better game overall, but people do not enjoy upgrading their computers.  These people may not be a majority, but they exist.  
I simply went and got a better video card.    It wound up being a real bear to get the skin viewer to work with it.   I still don't know what I changed to finally fix that issue.   But it works now so I'm not changing anything.  Lol
I also no longer play and numbers are the reason.   I keep my sub and still work on skins, but my time flying is zero.   I intend to see about changing that soon.   If people can make their presence known then they might intice others to stick around.