1. According to Faranak Margolese (“Off the Derech”) the most common reason why people go OTD is because of negative religious figures. In fact, I personally know someone who went OTD (and baruch Hashem came back) because of the blatant contradiction between what his father preached and what he sold in his business.
2. Becoming BT does not change one’s basic personality. Each person becomes the type of frum Jew that parallels what he was in his secular life. For example, an academic type will be drawn to a yeshivish life-style whereas someone who is more emotional will be drawn to Chassidut.