In retrospect years later, I think most of us wish we'd quit cold turkey as soon as we realized it was all BS, or even when we originally had misgivings. I know I do. Occasionally someone brings out their wife or children by slow-playing, but I think that's the exception rather than the rule, though there have been plenty of examples here.
Leaving has always been difficult. WT manipulation runs deep and goes beyond believing in their doctrines. If you follow their directives, you have no friends, no life, no nothing outside the organization. Everyone outside has impure motives, is vicious, and waiting to take advantage of you. If you leave, you are doomed to a life of materialism, drug abuse, and STD's. Fear and guilt are their most powerful motivators, not love for fellow man or a paradise earth.
Especially if you are a born in, the repetitive indoctrination trains you much the way it trains a dog. Perception and expectation have a bad habit of becoming reality. For every 18-30 year old JW I grew up with that left it behind and found their way relatively easily to a better life, I know 4 or 5 that became exactly what the JW's said they would: drug abusers or deadbeats or "immoral" with multiple children by multiple partners outside of marriage. Expectation becomes reality because most are unaware of any alternative. In the face of that, it's hard to leave if that's the only reality you're presented with.
I heard from many people when I was in, "Even if this wasn't the truth, we wouldn't leave, because this is the best way to live." And before the internet, when all you had to go by was observation of individuals who left your local congregation or circuit and what you heard from the platform, it was easy to believe.
I would like to think it's a little bit easier now with the internet. There are now countless examples of those who left and have had successful and happy lives. There are many places, such as this forum, to find support.
But at the end of the day, they still have your family. They still have your friends. They still have your whole way of life until you create a new one, regardless of if you believe their teachings any longer. And the fear of the unknown is the strongest fear of all.
Fear of the unknown can keep people sitting on the fence for a long time.