Movie characters hang up the phone earlier than actual people would.
I’m not sure this is wrong, per se. Movie dialogue in general is a heightened, optimized version of how real people talk. In many of these examples, adding a last goodbye would feel odd.
As the last few examples show, “thanks” has become an acceptable closer word in English. And “love you/love you too” often serves as a final couplet.
Still, I’ll be hyper-aware of phone calls both real and written for at least the rest of the week.