Because until quite recently, this knob mechanically influenced a bimetallic strip which simply shut off the power when it became too cold. I guess you cannot expect precise temperature control from this setup, so why lie to people? Also, you would need to manufacture different knobs for the US market.
Part of the world using Celcius, the rest Fahrenheit doesn't help for sure.
Whats the celcius part :D?
> Part of the world using Celcius
I guess "part of the world" is one way of saying the entire world except 2 countries.
or 30 percent if you use economic boundaries
A lot of Canadians will still give you the weather and pool temperature in Fahrenheit.