If you went into Eternals wondering why the MCU’s newest super-powered team didn’t do anything to stop Thanos’ snap, then you probably also care about plot holes.
Tasked with answering that question, Eternals fumbles the ball a bit, and it’s been noted that the film’s explanation might not hold up to scrutiny. At first, Eternals is pretty consistent with the existing canon: the Celestials that directed the Eternals on when to act were primarily concerned with Deviants, who were all killed off long before the events of Marvel’s Cinematic Universe. The Eternals have been around for some 7,000 years and only slightly nudged humanity toward the present day outside of fending off the Deviants. That all makes sense.
But alas! Toward the end of Eternals, we find out the real reason for their inaction⏤and so do the Eternals themselves. It’s revealed that the superhero team’s real purpose in intervening against the Deviants and protecting the Earth was to usher in an event called the Emergence, aka the birth of a new Celestial. The Celestials didn’t call on the Eternals to intervene in major conflicts that might progress the species closer to the point of Emergence, like ones that might lead to a great technological advancement.
While war certainly makes for innovation, the plan also relied on a booming human population for the new Celestial, Tiamut, to feed on. And that’s where the problems come in, because Thanos’ master plan — eradicating half the living things in the universe — would set the Celestials’ plan back. And we don’t know if the Celestial Arishem could have seen through all the twisting timelines of Endgame to know if Thanos’ plan would fail or not.
Without knowing what Arishem knew, some threads remain loose, but the Celestials are playing the long game here. Assuming that humanity was halved, that’s only really setting the population clock back about half a century. According to the UN, the global population reached three billion in 1960 and four billion in 1974. Given that we humans are projected to have a total population of 8 billion people by 2023, that’s really only a minor bump for the Celestials’ timeline. Never mind that Thanos is, as the end-credits scene suggests, an Eternal himself.
In the end, the Blip that returned the snapped humans was enough to usher in the Emergence — and give us another Marvel film. Only time will tell how the Eternals continue to affect the MCU moving forward.