Most people who have enough credit to be denied for having too much credit won't need a car loan, or most people are still under being maxed out and are not willing to take on another loan, hence not hearing about it.
Basically there is only so much credit you can get for your income level. Just to make it easy, lets say your limit is 200k. You have a 150k mortgage, a 25k car loan and 25k available on your credit cards. If you apply for new credit, even while having a lets say 790, you will get denied.