I can answer why people join. They are promised things beyond what they know, and it is choreographed to make it look real. They use the Bible (out of context) to prove that such conditions are imminent, and they will tell you that it is about to happen. They use the Bible to prove that conditions such as just before the Great Tribulation are upon us. Of course, they will not tell you all the rules.
You start studying. If you go through the book at the beginning, you will get some idea of the rules you are going to have to follow (I did that). Of course, there is no way to locate sources that will tell you that the rules are totally bogus. You think it's reasonable--smoking and drug use are bad for you anyways, Christmas is commercialized, fornication spreads disease, etc. So you commit.
The problem is that they are not being totally honest. I have found no fewer than two layers of fraud involved: The Bible itself was put together by one cult, and then misinterpreted by another cult. The original Catholic Church assembled the Bible in such a way to promote their agenda, and left out portions that undermined it (and the fact that Jesus' teaching in parables worked fine for the bicameral peasants to get them to think for themselves but not for us). That gives us the concept of a God that claims to care about us (but an objective look at the Old Testament will prove otherwise).
On top of that, the Watchtower Society further twists the Bible. Russell was among the cults that also started in that day (Mormons and Adventists), and if his principles would have been upheld, the witlesses would have been more like those cults. Then Rutherford added to it, proving that holidays were bad and that field circus was mandatory by taking scriptures out of context. It grew from bad to worse, and the New World Translation was born that altered key scriptures to fit the doctrines. Now, they have the Filthful and Disgraceful Slavebugger that tells people that they need to obey burdensome rules.
Now, you have the recipe for a total scam. People without the Internet still fall for the specious logic, and they cannot see that the Watchtower Society has two levels of fraud. They get suckered in, and then they are hounded to stay in. Things are supposedly going to get better, if only they stay in and do more. They do more, but things only get worse. Eventually, if the person is kept single and isolated from the "sisters", the person is likely to decide to take the religion and shove it.
