My observation in being out 14 years is most if not all leave because of their own personal growth.
I understand the need to be an "activist" and voice frustrations...point out the fallacies of the teachings and the shamefulness of their policies. So in the overt demonstrations, I think it is more of a personal, public statement that some just need to say. I venture to say hardly any current JW would be swayed to investigate information from a loud and busy banner type ad. Just my observation. The cult mind is strong. Mine was...I didn't want anything to do with "apostates" even though I was questioning everything.
However I do think the public demonstrations do inform the nonJW community that all is not well with those nice people that come to their door every Saturday morning.
But the internet and youtube...everybody goes to youtube to find out how to do things. I've met so many at fests who just stumbled on a youtube that spoke to them. One thing led to another, they investigate the websites and they are out.