I was happy at times as a JW. But it was surface-level stuff. Thought I had lots of friends, I was part of something bigger, unified with lots of people who are fairly decent folks.
But underneath I was stressed as hell, I wasn't taking care of myself, and I wouldn't say no to the elders as they pressured me into more and more unpaid labor. That resentment was like a slow boil underneath it all. I think that is how it is for a lot of folks in there. They just can't figure it out as to why they aren't really happy in their religion, but they are bombarded with all of the propoganda that they are happy, that they are serving Jehovah, that there is no where else to go.
It takes either a shot of courage, or a bad experience at the hands of another JW, preferably and elder. A WTF moment can help them stop for a few seconds and say "This shit isn't right, and I'm not going to sweep it under the rug"
The literature can do this too, and the nu light stuff. But they have to be paying attention, and we all know that JWs don't pay much attention to their own doctrine.
I do agree with Hassan though, if they are truly happy in the cult, there really isn't going to be anything that we can say or do to help them see the light.