Because it is the human scale for temperature. It turns out to not matter that much. but imagine a cold snowy winter, that's 0 and image a hot summer that's 100.
Really both C and F are silly, the minute temperature was found out to have a zero point, they should have been discarded, and we should have gone full in on Kelvin(or Rankine if that is your jam), or even better a new unit that better integrates 0, a scale from 0 to the boiling point of water? and give water boiling 1000? or would it be better to give water freezing 1000? Triple cells are a common way to calibrate temperature.
Yea but the scales don't match. 0-30 isn't very metric, whereas 0-100 is. If you added Fahrenheit to metric I think you'd be much more consistent.
Of course both scales can go above and below the numbers mentioned above, but if you are going to do things based on units of 10 you might as well be consistent.
0°F to 100°F spans the full range of temperatures I'd go out in & not consider it "extreme weather", so it's rather intuitive in that you can think of it as "how hot is it on a scale of 0-100". It feels very human centric & convenient for everyday usage IMO.
