Because it was a lie and the lie was being accepted as a truth without any facts emerging.
Same with the "decapitated babies" stories. I fell for it briefly, as did many others on here, but again, there was little evidence to prove it was true, but by then it was already accepted as "fact" and condemned. Same thing happened here, yet whilst we all rolled back on the babies story, some are reluctant to roll back on the "intentional hospital bombing by IDF" one, even when the same amount of contrary evidence has been provided.