cars are barely efficient in terms of time. In cost terms, cars are incredibly expensive once you add in infrastructure costs, insurance, fuel, the cost of land use, etc.
Public transit is efficient even outside areas of high density - see suburban Europe or India. Why are so many people here utterly car-brained?
Have you ever actually been to Europe? Public transit is pretty good in first-tier cities like Vienna / Stockholm / London where tourists spend most of their time. But out in the smaller cities and rural areas where regular people live there's very little public transit except for slow and inconvenient buses. So everyone drives. Or if they're too poor to afford a car then they just don't go anywhere.
This is my observation as well, it's also true in the USA. Places like Chicago and NYC have good public transit. You can easily live there without a car, in fact it's easier and certainly cheaper to not have to deal with owning a car. If you visted NYC and formed your impression of public transit in the USA based on that, it would be very wrong. Likewise you cannot assume that because Copenhagen has great public transit and bicycle infrastructure that all of Europe is like that. Get out to the smaller cities and towns and you'll find that many more people own cars and drive everywhere.
Public transit is efficient even outside areas of high density - see suburban Europe or India. Why are so many people here utterly car-brained?