I would think because an AI could be a perfect liar and good at deception, basically a simulacrum of a human - mimicry that a predator like a vampire would need to blend in enough to be able to hunt.

Here I was thinking it is because they require the "lifeblood" of others (the writings, videos, etc. which are uploaded by so-called "content creators") in order to exist. I like your description, too.