I think it is because 1- Flamels are long-lived, their minds would be probably wel-protected and 2- Voldemort was in a BAD shape at the time.
I read a story of Harry meeting the Addams and becoming Wednesday's boyfriend. I can't say much about the story, but I did enjoy the idea save for one point...
The author made Harry be a psychopath and evil since a kid. Dumbledore had been forced to brainwash him and all the Dursleys but Vernon (he explicitly says it would not be needed for him) to treat him badly and so he acts normally, and needs to reapply them from time to time because Harry breaks the brainwashing from time to time.
That really sours the story to me. Why can't Harry just meet the Addams and get along with them, just shrugging and accepting things since they aren't hurting anyone else, without needing to be mentally unstable? We had an old... ok, a children's cartoon, where a child befriends them.
I mean yes, in the movies the boy that tried to date Wednesday ended up being tricked by her and presumably being either scared away or scared dead, but it was clear to me even at a young age that he only did all that for her to get in a relationship with her, not real acceptance, and I doubt she would just roll with it now that he wasn't useful.
But while I admit I didn't see all the movies and tv series (well, I assume I didn't see all the movies, maybe I did... were they only three?) this movie and when there was a zombie trying to kill Gomez were the only cases I saw myself where they went to actually malicious.
Been thinking about trying to write my own version of the story. One where, instead of Harry being psycho, he just rolls with it, like he rolled with the Weasleys' own eccentricities... just, you know, more. Been thinking of doing it on Fifth Year instead of the Sixth of the mentioned fic too.