Hypothermia can be a problem in temperatures as high as 50F. 0F is a meaningless number, outside of purely subjective “it’s cold” uses.
“Can be” Yeah if you’re submerged in 50F water you will succumb to hypothermia due to the specific heat of water.
But we’re not discussing swimming pool temperatures, we’re discussing air temperatures. You are not actively in danger of imminent hypothermia at 50F air temp like you are at 0F air temp.
But of course you know that already. You’re not here arguing in good faith, you just want to sling shit at people that have a better understanding of the world than you. If you want to use Celsius for everything, go ahead. No one cares. But the intelligent world will keep using both.