It's a cosy social club. The doctrines don't mean a lot and they are always changing.
The rules are that you must never say anything against the cult leaders. You can have loads of friends but to join you have to leave common sense behind and adopt a paranoid stance of imminent doom for the rest of mankind while you swan into paradise.
That's why people in the West are not inclined to become members anymore, as the world rapidly becomes more educated, the JW beliefs are looking just too ridiculous.
If you were "born in" then along with the guilt about leaving and the fear of losing family support, it's easier for some to keep drinking the Kool aid and try and get what enjoyment they can out of life. Why go through life dragging this ball and chain?