First you need to understand that reality cop shows never show the whole incident. There is a lot of interaction that gets cut and only the "good stuff" get aired. 20+ minutes of roadside investigation isn't very entertaining to most folks. So, you never really get the whole story.
But, to your questions...
No, the driver couldn't have just walked away. The officer already saw a violation and was conducting a traffic stop for it. Just because the guy managed to get out of the car before the officer could catch up to him doesn't mean it's kings-X. Try putting that logic onto something more serious. Say a cop sees a guy robbing a bank. But, before the cop can get across the street to intervene, the guy completes the robbery and is now walking down the street. The robbery is over and no crime is currently being committed. Now the guy is just walking down the street. Does the guy get to just tell the cop "better luck next time" and keep walking?
Sure they could say that...but so what? The cop already saw him driving the car and committing a violation. What does it matter who the car belongs to? Do you mean could the guy just say "it wasn't me driving?" Sure, he could try that...if you really think the cop is that stupid.
If he had tried to just walk away from the cop, the cop would have stopped him and, possibly, arrested him for delaying or obstructing...using whatever force was reasonable to do so. Maybe a sternly delivered command would be all the force needed. Or, if the guy wanted to resist vigorously enough, maybe a good Tasing, bounced on the sidewalk, and handcuffing...trust me, that is not the way you want to become a reality TV star. Now, that would have made it on the air!
Behind the badge is a person. Behind the person is an ego. This is as it should be, person at the center and ego to the back.