It's a mind set thing. They are captives of an illusionary concept. That they are "The Faithful Slave" of Matthew 24:45-47.
That they passed the test of examination by Jesus 1919 and were appointed by him at that time.
So, when people who have checked this historic 1919 time frame and this doctrine which all others rest, and fine that it is not true, then leave, the WTS. cannot accept their reasons for leaving.
If they did accept the reason about 1919, down would come the whole WTS. structure.
This is from Captives of a Concept, by Don Cameron.
Blueblades