Everybody was there to have a good time - to some people, you can't have a good time without drugs or alcohol. Be that as it may, somewhat like the tragic soccer stadium fire in England a few years back, people having a good time even clear-minded are rendered incapable of recognizing impending doom ("it's all part of the show - how can this be happening?"). I don't think the effects of drugs and/or alcohol had any bearing on the decision-making with regards to the performers but certainly must have had something to do with so many people attempting to flee too late.
I've read many stories about this horror today, but the saddest by far, is to simply read the names, ages and homes of the victims. So terribly terribly sad, even moreso because so easily preventable.