Why would anyone opt to stay when they could be taken to safety in a few minutes and help was right there?
Perhaps they were concerned that helicopters are not exactly safe, especially in hot, high elevation conditions.
Remember the 1980 eruption of Mt. St. Helens. There was warning that something dramatic was about to happen but some people refused to leave, including an old man named Harry Truman. The ditzy governor of Washington encouraged him to stay. He was never seen again after the eruption and is presumably buried many feet underground.