In my last first aid class CPR was taught with compressions only. The reason behind this was that without proper, regular practice the pause for respiration may cause the blood pressure obtained with the compressions to drop below a required level.
A SAM splint does not take up much space and can be formed to fit narrow available space. A splint may help to control pain and keep a person with a broken arm more mobile and in better shape.
Basically it comes down to priorities.
If it isnīt broken, it doesnīt have enough features yet.