There is another set of users of the Global Sacrifice System who bear a bit of consideration, and they are the Old Ones. They are users in the sense that this is an agreement into which they’ve entered with humanity, in order to get a continuing IV drip of (to them) pleasurable abject suffering and death. This isn’t an imposed frame on the story. The ritual spoken by Sitterson are not the words of a zookeeper managing a downed animal’s Ketamine. They’re the words of a supplicant.
As long as the organization keeps the sacrifices coming, providing the tasty intravenous drip of human suffering, the world is allowed to continue as it is for another year. With this in mind, we can analyze how the system works for those users, i.e. the Old Ones.
The outputs that the Old Ones read from the system are unavailable to us, but we can tell it’s kind of precise. There are allusions midway through the film that the titan below the cabin is somehow “watching” the sex scene. (Though that ambiguous line could refer to the ravenous horror-movie audience as well.) It can also somehow sense the suffering of the victims, and whether the details of the ritual are being carried out in the proper order. The way we know this is that when Marty’s “death” vial is inappropriately shattered, the titan causes an earthquake that rocks the complex and the cabin.
This, then, is the input that the Old Ones have: shaking the ground in their displeasure. But as a signal, it’s far too vague. Hadley and Sitterson feel the quake, but disregard it. Hadley shouts, “They must be getting excited downstairs!” and Sitterson replies somewhat jadedly, “Greatest show on earth.” Had they had any inkling that they had actually messed up (even absent of what precisely was messed up) they would have pulled out the stops to find the error and correct it.
So while we as an audience are all in favor of resetting of a world that has accepted annual ritual sacrifice of young people, neither party to the agreement—the Old Ones nor the humans—set in place a system of communication that is precise enough to keep the agreement going. And that’s a failing of the interface.