Because they're human. They've evolved from a lineage whose biggest advantage was that it was social. Genes that could result in some large proportion of serial killers and genocidal tyrants are mostly purged. Even then, a few crop up from time to time.
There is no filter in the AI that purges these "genes". No evolutionary process to lessen the chances. And some relatively large risk that it's far, far more intelligent than a 70 iq point spread on you.
> There are power structures and social safeguards going back thousands of years to forestall that very possibility?
Huh? Why the fuck would it care about primate power structures?
Sometimes even us bald monkeys don't care about those, and it never ever fails to freak people the fuck out. Results in assassinations and other nonsense, and you all gibber and pee your pants and ask "how could anyone do that". I'd ask you to imagine such impulses and norm-breaking behaviors dialed up to 11, but what's the point... you can't even formulate a mental model of it when the volume's only at 1.6.