For me I know it was because I was a reader.
I began reading books at the age of 13, this was in the 1950's. Because there were some serious family problems I had two escapes I could count on reading and associating with my friends at the Kingdom Hall.
As I devoured Steinbeck, Hemingway, Wolf etc. My world view expanded....it had to. At the same time I realized that many of my friends young and old in the congregation never spoke of books or ideas. In most of our gatherings we spoke about other people. Apparently a steady diet of WT writing and meetings dulled the palette and discouraged curiosity. My first doubts about the WTBTS began to surface. I guess the brothers were right when they tried to discourage me from reading.
As my childhood years went by I continued to read and question but this was pre internet and pre Franz. I was no scholar and was loath to go to the library and read about other religions or compare scriptures. I already felt overwhelmed by my theocratic activities and underwhelmed by the witness life style. Then A friend loaned me a copy of Eric Hoffer's The True Believer and it was the life line I was looking for. Oddly enough it never mentioned the JW'S it didn't have to. It presented disturbing insights into other controlling groups and the reasons for the mindset of the organization and it's devoted followers. Finally I could put words to what had been observations and feelings.
Later the Rise and Fall of the Third Reich convinced me that god didn't care. It didn't matter if they were Jews, JW's or Gypsies god didn't care, or if he did, he couldn't or wouldn't do anything about human suffering.
One final book finished off my childhood belief system, James Michener's The Source which is a historical novel of the history of the Jewish people told through an archeological dig. It was an excellent read, very enjoyable as well as informative but two things really struck home. He was very critical of a religion (nameless) that tried to pass off Jehovah as god's name, a position I agreed with as I had always been embarrassed by it's miss use and thought it as ill conceived as inserting science into the name of the 19th century Christian Scientists. Why go out of ones way to play the fool?
The second thing that struck home was just how far back the history of the Jewish people went and how long they have persevered to protect their beliefs. After reading that book I concluded that the JW's were a poor version of god's people, childish in comparison, too silly to be taken seriously.
I was out at 23. Decades later I still read daily.