[DerKommissar]

The problem is one of statistics.

Whenever they pull someone over, which is often, they have to judge what you're going to do. For them, the chances of you doing something crazy like speeding off, pulling a gun, etc. is not insignificant. That's what they're thinking about when they're walking up to your car. They've been trained about what things to look for. And getting out of your car is the way many violent interactions begin.

If you just get out of your car and act nice, I doubt it could really be a problem. It's just a dicey thing to do, making any sort of act that could be perceived as aggressive towards an officer.

[vacri]

I have found the police to be politer and less patronising when I'm standing out of my car talking politely than when I'm sitting in my car at random traffic stops. Also, where I am, people are not armed as a rule, so fear of guns is there, but at a minimum. If having guns means you have to be too scared to get out of your car for fear of arrest, I'm not interested in having them. It's a somewhat ironic twist that the whole purpose of having an armed population in the US was to keep government authority in check, but here at the coalface of government authority, it gives them even more power out of fear.

And getting out of your car is the way many violent interactions begin.

It is, which is why you remain polite. It's not going to work if you're angry. It does (usually) change the way they talk, since on their part you now need to be managed, which means not going on a power trip. Remain friendly and they won't fear for physical safety, and you're now in a conversation where you're much less a submissive.

[nopassrecover]

"since on their part you need to be managed"

You have been very lucky to get reasonable officers. Most I have talked to (or seen in media / documentaries) have been trained to escalate with force if you are not submissive - get out of your car leads to "GET BACK IN THE CAR NOW HANDS ON THE WHEEL", answering back ("Why? I'm doing nothing wrong") leads to verbal escalation/shouting, shouting yourself leads to handcuffs, resistance (even passive) to physical force or (according to media accounts) tasering. Granted my sample size is potentially biased, but I thought this was the norm. On the other hand, when I've been relaxed, calm, and collected while remaining in the car I've had no issues and otherwise pleasant conversations with officers.