Because, as a wise woman recently said, "That is very shoddy scholarship for someone who's supposed to be so influential." That and the fact that Carrier has had actual correspondence with Flew, so there's a relationship there. Why shouldn't he be frustrated with him over this?
I assume you're trying to imply that Carrier is secretly frightened that (horrors!) God really does exist and now he has to stop participating in the daily drug-induced sex orgies that all us atheists must surely be engaging in behind your back? Hardly.
If I really, really didn't believe in God I would not care one whit what someone else did nor would I jump on him if he were unable to fully articulate a change in the reasoning. In fact, I suspect I'd be a little like Voltaire in seeking sincere believers for those I hire with the reasonable expectation that they would be more inclined to show up for work and less inclined to pilfer.
the daily drug-induced sex orgies that all us atheists must surely be engaging in behind your back?
Here. Read this.