HI LUCID CHIMP:
Your question is not stupid. Most people leave the JW religion either over doctrine OR mistreatment.
If a person is disfellowshipped and decides NOT to seek reinstatement, one of these reasons (maybe both), have played a part. Since a DFd person has a lot of time on their hands, they may do a lot of research or take college classes. They may reconnect with blood relatives and non-JW friends. They wake up and realize they were in a self-imposed prison in the JW religion and wasting their precious time and lives!
I am a "walkaway" and my reason for leaving was a combination of their bad attitudes plus that they deceived people. I could not continue. The 1995 changed teaching on "Generation" did it for me.
Am I glad it's over? You bet I am.