Driving is dangerous. That much is a commonplace. When you pilot 4,000 to 6,000 pounds of steel down the road at highway speeds, bad things happen when you drive too fast and lose control.
It probably seemed like something a "cool dad" would do. Give the keys to your Suburban, to your 15-year-old, unlicensed daughter. You were on vacation, it was a quiet morning, she would run with her friends to breakfast and bring you back something.