Part of that is because the franchise is far from ending with multiple spin-off shows on the way, and with a decent amount of time in the finale setting them up.
“There was a scene that we had shot, but when it was decided to put the coda in we felt like it would conflict with the Rick and Michonne bit.
“After Daryl rode off, we cut forward to the Freedom Parkway, outside Atlanta – where the iconic shot of Rick rode down from the pilot.
This is Rick Grimes.” (Which, of course, is his name – and the line Rick said in the pilot.) Then we end with the voice of a survivor answering back: ‘Hello?'”