Av8r:
I think mostly it is related to being able to diagnose things better, realise what's going on and begin treatment. There is a difference between stopping things getting worse, stabilizing, and commencing the fixing up phase.
It's been said The "Golden hour " concept only changes outcomes when the fix-it phase is started within the hour. Stabilizing or slowing down the demise doesn't seem to alter outcome. That might be as "simple" as fluid resuscitation - but also might be complex like the choice of pressure control ventilation vs volume control ventilation. (These are modes of ventilating someone (a level of complexity higher than just sticking tube down their neck and sqeezing a bag) or beginning heart optimizing drugs and deciding on which one depending on what else is going on with the patient - do you choose Alpha agonists or beta agonists (different types of heart drugs) or nitrates.
Similarly there is a better appreciation of what's going in this patient with the rest of their systems. Being able to look outside the algoriths and protocols.
The other thing that I saw in some of the juniors was a failure to appreciate the significance of things simply because the level of knowledge wasn't there (from simple lack of experience.) Sometimes a little knowledge was not enough for people to realise they were not equipped to handle where they were taking themselves. The classic is the (and I have personally had to rescue patients a couple of times) when the proper treatment is to intubate and ventilate and the guy on the scene knew that - fine- got out the drugs fired them in - patient paralysed - then - couldn't intubate! Bag and mask - couldn't ventilate! Patient has three minutes to live.
Operator knew how to sling a tube in the easy "normal"patient but these were not easy nor normal but his experience wasn't enough to work that out. Fortunately these were while we in the resusc rooms in peripheral hospitals and when I took over and used some tricks we got out of trouble but...... these are tricks I learned as a specialist over fifteen years.
Overall it's a mix of things mostly related to experience and training at looking after patients with these problems every day (and doing from start to finish not doing just the front bit and then handing over to someone to sort out the primary disease and any complications that can happen from the treatment.)
Same reason any patient in any field of medicine is statistically likely to do better with a specialist rather than junior with limited experience.