Why Bother making a Eternals movie. If your not going follow the Source Material at all.

Indoctrination.

It's inculcation through cultivation theory.

Eternals isn't a very popular or widely known comic book, but the MCU is the biggest movie brand in the industry right now, so everything they touch is considered gold.

Eternals gives Marvel (and by proxy, Disney) the opportunity to start reorienting the way material is presented to the broader mainstream audience by pushing in Left-wing propaganda more prominently, hence why one of the biggest topics surrounding the Eternals -- even before any trailers were made available -- was the interracial gay kiss between a black man and a Muslim man (something neither demographic is interested in seeing).

Now that they have a global audience hooked after ten years of (arguably) quality made movies with an over-arching storyline, they're now focusing on brainwashing people with Left-wing degeneracy.

Expect to see a LOT more of that kind of propaganda in their newer phase 4 films.