Because the video captures the exact moment civilization leaves the room. The hotness is the voyeuristic thrill of watching an audience go utterly feral.
However, as the hours passed and the artist remained passive, the atmosphere shifted drastically. The "hot" intensity of the performance escalated from curiosity to cruelty. The absence of resistance emboldened the participants. Clothes were cut off her body with the scissors. Her skin was written upon. The violence escalated to physical torture: her hair was pulled, she was cut with thorns, and her neck was sliced. The culmination of this aggression occurred when a loaded gun was placed in her hand and her finger was positioned on the trigger; in that moment, the audience was holding the potential for murder.
The "hot" in that video is not a temperature. It is the sweat beading on her immobile face as tears finally cut through her stoic mask. It is the reddening skin where glass shards are laid across her chest. It is the white-hot line between performance and attempted murder. When the six hours ended and she walked toward the audience, her body still bloody and marked, they fled. They couldn't face the heat of what they had become.