Screen Rant
When Eternals debuted in the MCU many wondered if the new heroes were to eventually join The Avengers franchise, but they're actually more akin to The Guardians of the Galaxy–and should stay that way. The Avengers are left in a state of disarray after the events of Avengers: Endgame. With Captain America, Iron Man, and Black Widow out of commission there is much speculation as to who will lead Earth’s Mightiest Heroes next. Audiences suspected that Ikaris or Sersi could now lead the Avengers, but given what happened in Eternals, that is not likely because Marvel needs them to fulfill a different purpose.
Eternals revealed that their superhero team was created by the Celestial Arishem to prepare for the Emergence, or the birth of a new Celestial being, which would destroy the earth in the process. By the end of the film, Sersi and several other Eternals had foiled the Emergence, but Arishem then abducted Sersi, Phastos, and Kingo into a space singularity to answer for their actions. The post-credits scene revealed that, aided by Thanos’ brother, Eros, Thena and Makkari vowed to find their lost comrades.
If and when the Eternals are reunited, however, they shouldn't join any future Avengers movies. The MCU needs a superhero team that is entirely set apart now that the Guardians of the Galaxy have fought alongside the Avengers. Before the events of Avengers: Infinity War, the world of the Guardians was separate from that of the Avengers, and plenty of audiences even thought the Guardians of the Galaxy were better than the Avengers. However, after Thanos’s journey to find all the Infinity Stones, the Avengers and Guardians essentially merged to fight Thanos. Now that the teams are intertwined, Marvel needs the Eternals to be the new separate team of superheroes that the MCU can use to explore non-Avengers-related adventures.
Plus, the Eternals becoming Avengers would ignore many plot developments in the MCU. The thin excuse that they couldn't act unless it directly related to the Emergence was fine in their own movie, but if they mingle with the wider Marvel universe, that question will keep coming up. To avoid creating a messy plotline where various threads would be dropped, the future movies surrounding Eternals should focus on a separate story.
The Eternals also need to remain separate from the Avengers for now in order to fill the hole in the MCU left by the Guardians of the Galaxy. Before Infinity War, the Guardians didn’t have much to do with the earthbound team beyond showcasing the occasional Easter egg. Now that the teams have connected, the Guardians will likely be dealing with the effects of Avengers: Endgame as well as helping Thor in future MCU projects.
