I don't know anyone who keeps their license in their car. Car culture is different in the us vs the eu, so maybe not as common over there, but sometimes if traveling with friends you will switch who drives. You should have your license on you if you're driving. Additionally, it's good to have your ID in case you forget your credit card somewhere and now you have a document with your picture on it that has a name that matches the card. I still get carded sometimes when buying alcohol or entering certain places so it's not unusual to want to keep it on hand in case you want drinks or something.

Also good to have your ID and insurance information in case of an emergency.

Because a cop can stop you at any time, in any place for any reason and while (legally) you don't need to show it - your day will suddenly get a whole lot worse if you don't.

And In the year of our Lord - you must also worry about ICE

I might drive my car, I might drive my partner's, I might drive my coworker's car. I might collapse on the street and someone needs to figure out who I am from what I'm carrying. The license/id stays with me, not the vehicle.

The grocery store I buy booze at forces the cashier to scan your ID. Also I walk there.

If you need to use a car that's not yours, what would you do if the license is in the car?

And why wouldn't you carry your id with you? Not just police might want to stop and ask for it, but what if you get involved in an accident and have to get taken to the hospital while unconscious? How are they going to id you to know who to call? Just to say an example.

Also, your medical card should always be with you in case of an emergency. You never know when will you need to be taken to the hospital and having it with you makes everything much easier.

There's no advantage that I can think of in not carrying your documents (or even copies of them) with you.

Because in a lot of places you legally have to carry your ID on you, not just when you're driving.