Why are christians so desperate to deny those who became Atheists were ever christians? [Spirituality & Religion]

I used to be a devout christian but, after seriously studying the bible and examining my faith, determined it was all BS. I found the bible to be nothing more than a jumble of myths and superstitions taken from various older belief systems and frequently contradictory. As a result of my studies, I became an Atheist.

Now I find some christians are desperate to deny I was ever a christian. They just can't accept the fact that a christian could ever break away from "the truth" (as they like to call their beliefs) to become an Atheist. The idea is so alien to them they deny it's even possible. They even claim to know what the person experienced better than that person knows. Another claim is that I couldn't have studied the bible "properly" and that I should ask (their) "god" for help. What are they so scared of?