Well a doctor has a higher position than a nurse and likely has more responsibilities than a nurse. They're probaly just afraid that their nurses will mess up which will lead to the doctor taking the blame. Also I'm sure nurses know what theyre doing but im positive theyre still less...
Oh and also im glad Erina is finally in the center of character development, a tsundere who just actually had a tough upbringing and is really sweet from the inside <3 Way better than that boring girl called Megumi