Car drivers get trained when doing driving lessons. There are so many roundabouts that you have to cooperate as a car driver. Also, it is well-known that when an accident happens, the car driver gets the financial damage, and yes, the insurance will pay, but he/she will lose a big percentage of the no-claim decrease in insurance fee.
Recently, local governments are moving away from the real small roundabouts like this one because in the dark, when it is raining, with cyclists who are without lights, these are still somewhat unsafe:
https://www.telegraaf.nl/images/1540x866/filters:format(jpeg...
These are much more modern, and car drivers can more easily see cyclists and mopeds come:
https://www.denhaag.nl/upload/0690e94f-f7ac-43a3-8c1e-4fb768...
Oh, and yes, car drivers can sometimes be aggressive. The same counts for cyclists though. I guess both kinds of people are just like normal people. And by the way, a lot of people are one day car drivers, the next day cyclist, there is a lot of sympathy.