I think people complaining about the lack of their favorite characters have to realize that changes made with adaptations are often done in service of the story. They are different universes with different circumstances and different main characters, so things will play out differently and different characters will get focus. It happens all the time with franchises (e.g. Harry Potter, Game of Thrones, MCU, etc.), especially when you're limited with runtime.
E for Extinction may have been pivotal moments in the lives of characters like Polaris and Emma, but they themselves weren't pivotal to the overall story. Cut those characters out and the story would have progressed almost the exact same way. Would the emotional moments hit as hard if the audience had to follow characters they weren't familiar with as opposed to ones they have been following since the beginning? Probably not.