Police do not need probable cause to demand ID and if you are told to get out of the car and instead you remain in the vehicle and start reaching around for stuff, you are going to make somebody with a gun and a badge nervous. Review Chris Rock's "How not to get your @ss kicked by the police."
Many people apparently do not understand that LEOs have certain powers that regular civilians do not. When they give you an order, it is a lawful order and you are obligated to comply unless it is to do something that is clearly against the law.
Asking "why" implies that a lawful order is negotiable. It is not. You do what you're told; the police are not obligated to offer an explanation. If you do not obey a lawful order and demand an explanation instead, expect to be forced.
Be smart and stay alive.
Only a police officer has the legal authority to stop you when you are violating a traffic law, demand ID and initiate physical force for non-compliance. Citizens cannot do that to each other; only if life and limb are threatened can a citizen legally initiate physical force.
It is not optional for citizens to comply with lawful orders by the police. You are not asserting your "rights" by refusing to provide ID when demanded by a sworn officer. You are in fact in violation of the law when not cooperating -- and subject to physical force. And typically when people refuse to provide ID or claim they don't have one, officers can reasonably surmise that the reason is the subject has a warrant and/or something to hide. That, and rummaging around in a bag rather than getting out of the vehicle when ordered, is going to make a cop bust the window and tase you -- anywhere in the world.
Try to put away your personal biases, give the officer the benefit of the doubt and do your best to imagine the officer's perspective when you are being contacted by a LEO. Don't do and say things that would reasonably make them suspicious and escalate a minor traffic stop into something worse. A tiny bit of empathy might spare you being tased, cuffed and/or thrown to the ground.
The video that is being broadcast picks up when the officer is standing on the passengers side saying, "so you will not step out of the vehicle?" Then you can see the passenger bend his head down away from the cop. [You can't see very well, but that is likely when he was rummaging through a bag rather than complying with the order to open the door and get out.] Then the officer breaks the glass and tases the passenger.
We are not seeing the very beginning. Instead, the driver in the interview characterizes the initial contact as the officer was in a "bad mood from the start" rather than describing what was actually said and done prior to the start of the video. That makes me suspicious.
Given that the initial contact was about a seatbelt violation, and given that the occupants of the vehicle already were apparently disposed to think that lawful orders by LEOs are optional, IMO she was probably not cooperative and gave attitude to the cop when he initially approached her side of the car. If she did that, that was an unwise move that precipitated an unnecessary escalation.
I'll bet that she or the passenger were the ones who talked first. That part was not shown in the video. Neither she nor the passenger had their windows down when the video started. That alone indicates lack of cooperation.
Also, people who have violated the law will sometimes feign outrage with the hopes of disincentivizing the cop from proceeding further. [In some cases a true sociopath will become genuinely outraged when faced with limitations/consequences because they don't think they should be subject to rules that apply to everyone else.] In reality, becoming inordinately emotional about something minor like a seatbelt violation will make the officer suspicious.
Typically in a traffic stop, the officer will not even be on the passengers side of the vehicle. The fact that the video starts with the officer there indicates that the passenger gave the cop [through word and deed] a reason to move from the driver's to the passenger's side. I seriously doubt that the cop would have been there if the passenger kept his hands in plain view and his mouth shut.
If you want to avoid trouble with the police during a traffic stop -- and keep the encounter brief -- speak only when spoken to, keep your answers as short as possible, do what you're told promptly [don't give the impression that you are stalling] and keep your emotions to yourself.
Not if you're going to vote...