Because someone who has towed for years has likely faced things like sway, loss of control, overcompensation, and so on, and how the trailer affects them. They are more likely to react in a swift and effective manner than someone who hasn't experienced those things with a trailer hanging off the back of the vehicle.
It's not that EVERY longtime trailer hauler is better or more capable, but that the odds of a longtime trailer hauler having learned how to deal with a blowout without major incident is greater than the odds of a newbie doing so.
