The chances of experiencing a flat tire at some point approach 100% and unless you have a spare the failure is catastrophic relative to your ability to get where you’re going.I havent had a flat tire in over two decades either but I always carry a spare tire in my car just in case my tire luck runs out
Plus, cars are usually designed to accommodate spare tires without affecting the utility of the car. As in, you don’t have to set it in the seat next to you.
The chances of catastrophic failure of a bass are far, far lower and the “cost” of carrying a backup is much higher. I don’t think it’s a fair comparison.