The main reason was the generation back flip. For decades I had hammered on people's doors, hassled work mates and generally annoyed everyone that the generation that were old enough to recognise 1914 as the beginning of god's heavenly kingdom would see out this system and pass through armageddon into a paradise earth.
Of course I told people this as it was my belief, my basis of faith and really my "evidence" of a loving and just god. When I read that initial "new light" in the watchtower, I went numb. What made it worse was that none of my friends could see the change and speaking to the elders, I was warned about apostate thinking! Was I going mad? Only reading here on this site years later did I find out that the wtbts finally admitted albeit briefly that they had erred.