Fantasy promises, a great social network and belonging - thinking that your life would have greater meaning.
That's what gets them originally but as above no healthy well adjusted person with healthy self respect would join because they don't need congrats from others to be a good person, only the despots do otherwise the rest had no choice as children and you get stuck there out of guilt for family or friends.
It's not till later on you see the damage from the cult control. I have two very well balanced kids 22 and 19 who luckily for them did not get the brainfuck for too long - yay