Warning! Spoiler ahead for Eternals.
Marvel Studios' threat of the Emergence.
The Eternals have been on Earth for thousands of years. But, since they were not permitted to meddle with human tragedies unless it involved the Deviants, they kept to themselves and blended in. This was also the reason why they didn't interfere when Thanos (Josh Brolin) threatened the universe using the Infinity Stones. After operating as a unit for centuries, they decided to part ways; each Eternal went on to live different kinds of lives. Some of them kept in touch, but others lived in isolation. But, when Deviants re-emerge significantly evolved, the team was forced to re-assemble.
In Eternals, the first WandaVision.
What's uncertain is the whereabouts of Sam Wilson (Anthony Mackie), who should've already assumed the role of Captain America at this point. Based on MCU's timeline, the events of Wong (Benedict Wong), and by way, Doctor Strange. But since the Destin Cretton and Simu Liu film happened around the same time as Spider-Man: Far From Home and Eternals, it's possible that everyone was just too busy to get themselves involved with the Emergence, especially since nothing bad really came out of it.
As the MCU continues to expand, isolating stories from each other is getting much trickier. Phase 2 films such as The Avengers. There hasn't been any official explanation regarding those queries. However, while they were able to get away with it, the same questions will keep on popping up beyond Eternals unless they explicitly reveal where the rest of the MCU heroes are during a standalone story.
