It makes no sense because that's not what the 0 of the Fahrenheit scale is. The 0 point is the coldest an ammonium chloride brine mixture can be cooled to. The 90 point was an estimated average for human body temperature (it was adjusted up over time). These were chosen because the goal of the scale was to provide a way for people to have a defined temperature scale with a range and degree size that could be reliably reproduced without passing around standardized tools. 100 is really hot because human bodies were used as a reference for the high end, but the low end has nothing to do with the human body.