Because they aren’t ISIS, they’re a bunch of misguided otaku. Yes they are the baddies, so they’re gonna go all “Wooo, sacrifices!!”, but it’s basically a bunch of people dissatisfied with their own society who follow an over-the-top guru while wearing stupid black robes. None of the infiltrating another country to murder journalists and country-goers, destroying world cultural heritage, collecting rape-slaves and genociding religious minority that actual ISIS does.
I feel like "the 'misguided otakus' haven't done blank, blank and blank" has to be qualified with a "yet."
The "misguided otakus" had been performing blood sacrifices to try to bring about the end of the world. We'll probably never get the actual figure, but they'd apparently been feeding like a dozen people a month (if not more, really depending on how often they dared set traps) to a monster with the intent that the monster would power up and kill everyone in Tokyo.
So their preliminary body count is probably in the hundreds, with a target goal of millions and eventually billions because actual magic doomsday cult.
I assume they would have committed more crimes than just mass murder if they thought the monster would power up from it.
I suppose Aum Shinrikyo - the cult that released sarin gas in the Tokyo subway - would be a more appropriate comparison than ISIS, but my sentiment remains the same.
The whole damn lot of them belong in a grave.