It is known by this name for many reasons.
1: the male porn star usually takes an ungodly amount of time to finish his business.
2: because of the size of the video bar, an attempt at skipping any of the material would result in missing the finale.
And 3: because this is usually the period when someone watching pornography is reaching climax, leaving said person with their pants down.
Guy #2: "You couldn't just exit out?"
Guy #1: "No way, by then I was already losing it all over the place!"