Non veni pacem mittere, sed gladium.
The lead person has significantly more surface area in contact with the slide which results in more friction which reduces her velocity which causes the more streamlined persons to pile-up behind her which creates a single single mass-in-motion which exceeded the restraint capacity of the sidewall which failed when the unitized mass reached escape velocity and became airborne. Oh the humanity!
Too much speed and too much butt mass = disaster.
I'll take one of the clean ones for $100 Alex.