I think the reason for this is because many die hard JWs are totally incapable of understanding how a former JW can possibly just stop believing in the 'Truth' and therefore they treat you as if you are suffering from either severe memory loss or have somehow become completely stupid with the IQ of a toddler. This causes them to speak to you verrrrryyy slowly and patronisingly to ensure you understand the simple dumbed down 'witness' they are giving you. I can remember actually telling one particular sister that I had not lost my memory and that I knew as much about everything as she did, I just simply did not want to go to meetings any more.
Another sister was far more aggressive and yelled at me for being selfish and told me that it did not matter if I didn't believe it was the truth, I still had a duty to remain an active JW for the sake of my mother! I told her that this is exactly what I had been doing for many years, but could not do it any longer!!
I don't know which of these experiences was worse