They don't tell you about the things they do when you join. You have to study with someone for quite a while before you get baptized. Even then I was told that only people who committ very serious sins and are who are unrepentant and refuse to stop will be disfellowshipped. This was not at all true, but I didn't find that out for years, by then I was too brainwashed to leave.
Of course when I converted it was back in 1968, there was no internet and no easyway to check things out, plus I was only 13. I was attracted to the idea of living on a restored earth. My sister who was ten years older than me converted and that is what got my parents and I interested.
I think the internet is making it very easy for people to see what they are getting into, so they are not seeing the growth like they used to.