I go with the internet exposing them.
But it has come a few years after the "generation change" which has dampened spirits, and easy access to smartphones has come along to accelerate that.
1995 was actually the end of the "two horned wild beast" aka 1975 and the generation that saw 1914. This was really one doctrine with 1975 being the first disappointment and 1995 being the writing on the wall that the whole thing was a crock of shit.
But keen dubs could still hold on to the generation doctrine in their heads. My old study conductor actually said to me in about 1996/7 - "the generation doesn't really pass away until 2000 or even 2014 - I'll wait and see." Sadly he died in 2012.
So the generation change started a twenty year gradual disappointment for some older born-ins. That hope pretty much died in 2014 with the big hoopla conventions.
After 1975, there was still the "old generation teaching" going strong for another fifteen to 20 years and so a bounce back occurred. After 1995 nothing of urgency (except "soon") replaced it.
Internet.
The internet came into many homes on a PC in the early 2000's. Then laptops and then from the late 2000's handheld devices. (Remember the advice to have your PC in the family room so you couldn't privately access stuff?)
So I believe that in the west most folk got private use of the web from about 2005 and especially so since the late 2000's. This is increasing yearly even now and encompassing second and even third world countries.
Internet's effect on non-jw's who might have otherwise been interested.
All except the most emotionally damaged will quickly, after a visit from two nice ladies or an encounter at the trolley cart, check out JW's on line. When they do they will be met with jw.facts, child abuse headlines, shunning, blood and other negative stuff.
Only the slack-jawed wrecks will come in from the outside. This is why if you look round your KH you will see the dregs of society. The dubbies will say they are those sighing and crying. I say that they are the only ones left who cannot see this cult for what it truly is.
Born-ins - as evidenced by the newbies on this forum will also see the negatives and the poor kids will be stuck between losing their families and losing their sanity.