That's nearly three minutes of characters leaving people on the other line wondering if the person they were talking to was silently murdered. If someone was persistent or insane enough, that video could have been 200 hours long without ever using the same scene twice. This trope so consistently shows up in movies and TV shows that there has to be a legitimate reason for it, because right now, the only reasoning I have is that screenwriters are secretly telling us the characters we're supposed to empathize with are actually inconsiderate dicks. Since that can't possibly be right, why do so many characters refuse to say goodbye?
The answer can be summed up in a single word: efficiency.
A lot of screenwriters so strictly adhere to the idea that every word in the script must push the story and character development ahead that even little things like saying goodbye at the end of a phone call get sacrificed in the name of keeping the story moving ahead as smoothly as possible. "Every word in your script should mean something and move the story along," said one screenwriter, adding that leaving in little conversational buffers like "goodbye" can make a script sound "amateurish." To me it seems more amateurish to leave a small hole in the script that lets audiences think that the main character is a rude shitheel. The tradeoff doesn't seem worth it, especially when the thing being sacrificed isn't gonna stop the narrative momentum dead in its tracks.
I understand the reasoning, but why bother cutting that single, specific word? To move on to the next thing 0.7 seconds faster? I mean, even after "goodbye" is cut from the script, we still end up seeing the 1.3-second shot of them physically hanging up the phone. They didn't say goodbye, but at least I know they have basic cognitive functions and motor skills. I am now very confident they have what it takes to defeat the alien invaders.