Why would they do it?
Short answer: they are in love with their own power, and they don't give a shit that you are suffering.
They did the same to my son; first of all, no egregious sin, just went to them a second time to admit to something he didn't tell them the first time.
No repeat sin; just felt bad that he had held back.
Incredibly, they df'd him over it.
Then they dragged their feet for months when it came time to reinstate, missing appointments and not responding to letters.
He was devastated by their complete lack of compassion.
I admire your persistence in pursuing reinstatement for your family. It is something I would do if in your position but I know I would never get over having to grovel to the little tin soldiers that run the kingdom hall.