Some here think it gives them some sort of credibility when they criticize the Church, to claim to have been members in the past.
They trumpet, “I saw the light, now I know the truth” and it’s as phony as a three dollar bill. They cannot even describe the Church accurately, have no idea about scripture in the mass, never knew Catholic teaching about Mary, and claim that the Bible is their sole authority. Those people were never Catholic. You can say it’s midnight at noon, doesn’t mean anyone with eyesight will believe it.
There is another possibility: they were kidnapped, brainwashed and had false memories implanted by some cult. I can't think of too many explanations that suffice to describe what they claim are their experiences, as far away from reality as tribesmen in Borneo are from Iowa.