I think a big factor is the increasing prevalence of DF who don't ever come back because of finding out about the other side while out. My brother and two other friends of ours are in this category.
Until I left, my brother still thought they had the truth and would have encouraged anyone looking into the Bible to study with Jehovah's Witnesses. He was very proud of his daughter's first student talk. Now, he can explain to anyone why he will never be a JW again, and why he would encourage them to look elsewhere for Scriptural understanding.
He got a call from his daughter a couple of weeks ago telling him that she is getting baptized at the next Assembly and won't be talking to him anymore. Her mother and my wife are firmly opposed to her decision, but my extended family are all glowing and atitter (<--- love that word, for some reason ) with praise for her because she has "taken a firm stand for Jehovah." [Urp!] Sorry, I just spit up a little in my mouth.
Anyway, I think there is more than just one piece to this thing. People who used to never be in contact with "apostates" and were unlikely to ever meet one are now only one or two mouse-clicks away from more information than they could absorb in a year.
I expect the tilt toward higher percentages of DA to get increasingly sharper over time.
Respectfully,
AuldSoul