Why does the fridge thermostat have an inverted scale?

In all fridges that I've ever encountered which had a manual thermostat, the scale on the thermostat was a scale of "inverse temperature":

• 1 means keep the fridge hotter
• 5 means keep the fridge colder

Why is it like that?

Note that on the manual the producer "cheats", specifying it's a scale of power (5 => more power => colder), but of course the actual knob controls a thermostat.

(Of course, modern fridges don't have a knob any more and they just set themselves to 3-4°C.)