| Because water is arguably the most important substance to mankind. In the celsius system (and at standard pressure and bhawawa please point out technicalities) - water freezes at 0°C and boils at 100°C. That's pretty simple to remember and makes actual sense. In fahrenheit, body temperature was supposed to be 100°F but its not because when the guy measured his temperature, he had a fever. Congrats dude. First strike. It freezes at around 30°F but not quite. The scale just doesn't make sense for any intuitive application. If you think that body temperature should determine the scale of temperature measurements, think about how often you need to know your body temperature vs. how often you need to know how hot it is outside. "is it tornado season? nah, its only about 0.7 body temperatures outside". Besides, to anchor a scale, you need 2 reference points. Not just one. Fahrenheit is just a turd. On top of that, Celsius scales just like Kelvin. 0 Kelvin is the point of absolute zero. The point of "No temperature" - to keep things simple. 0°C is 273.15K and 100°C is 373.15K - which means that Celsius is essentially Kelvin (the unit that makes scientific sense) adjusted to a level that makes sense for common man applications. That explains why everyone is using Celsius. Nobody can tell you why the US does not. Its clearly because they are some very special snowflake. Same reason they use retarded units like inches, feet, yards, miles, ounces and pounds. Metric systems be damned. |
After his death in 1776, it was redefined based on the freezing and boiling points of water at STP, at 32 and 212 (a difference of 180). So in fact it uses the same fixed points as Celsius, and has for hundreds of years.
Also, you have Celsius and Kelvin backwards: Kelvin was originally formulated to use the same sized degrees as Celsius, not the other way round. Celsius was first. (Although Celsius is now defined in terms of Kelvin.) See also Rankine, which is the Kelvin equivalent to Fahrenheit: absolute zero is 0, the freezing point of water at STP is about 492, and boiling point is about 671.
Did you know that the original Celsius scale ran from 0 at boiling point to 100 at freezing point, i.e. backwards? It was reversed after his death. Fahrenheit didn't make that mistake!