If it's their vehicle and the vehicle wasn't stolen, the owner should know who was driving it. Courts do compel people to testify sometimes (when it is not self-incriminating).

They are not required to know who is driving their registered vehicle at all times, just that anyone that is allowed to drive it has a license.

What are some scenarios where a vehicle owner knows that the vehicle is being driven by someone with a license, but not who that person is?

Happens all the time. You and your spouse do the same or similar route (e.g. bring child to school) and a month later you get a ticket. Who was driving that day?

You have one spouse and several children, and all of them have a license and are allowed to use the car?

Your court date will be weeks after receiving the citation in the mail. Most families talk once in a while.

The state is constitutionally unable to force you to testify against yourself because the judge ruled these tickets are quasi criminal