It seems that most XJWs have left because at one point in their JW life something happened that made them start to think something wasn't right with the religion. When I left, I still believed the JWs had "the truth". I was dying inside, trapped and unhappy (another poster's words, but describes exactly how I felt). I HAD to get out of my current life. It was a matter of survival.
I wrote a letter to DA myself for a couple reasons. 1: I knew that leaving and how I did it would be a DFing offence. I'd already been there, done that and didn't want to mess with the whole JC thing again. 2: I removed myself from being a JW to protect Jehovah's name. I didn't want to bring reproach on the cong. for my actions. Co-workers etc. who knew I was a JW would soon find out that I had left my husband...
At the time, I was escaping my unhappy marriage and a life that was going nowhere. If I could've done that and remained a JW, I would have. For a long time after leaving I defended the JW beliefs. It's only now, 7 yrs later, that I'm starting to realize that I was leaving my religion, too. I envy those who figured out the falsities which then propelled them to leave, either physically or mentally/emotionally.
Edited: Just to avoid further comments regarding the WT having "the truth", I would like to clarify that I no longer believe it's the truth. (Does anyone on JWN?) That thought dissolved about 6 yrs ago for me. The OP refers to my mind set at the time, not now.