Trauma 1 is the highest level of Trauma and only certain hospitals are certified as "Level 1 Trauma Centers"
In Utah, and large portions of surrounding states, IMC and University are the only Level 1 Trauma Centers...thus the large helicopter and plane fleet.
One thing you need to remember, people are categorized by EMT/Paramedic personnel not only on their visible injuries and symptoms, but also method of injury.
A person may look fine, may feel fine, but be transported to a Level 1 Trauma center because of the method of injury. That does not always require a helicopter (There actually is a guideline for when helicopters are used, check out this website for details University Health Care AirMed Criteria for Air Medical Transport
) Of course weather etc also plays a role.
Now, IMC and the U are routinely on what is known as "Trauma Divert", which happens when they already have too many Trauma patients or their ICU's are too full.