Well because it stands on a false promise. Neither 0°F = the freezing temperature of a solution of brine made from a mixture of water, ice, and ammonium chloride nor 100°F has any „real“ meaning.

It’s not about the specific numbers, but the range that they cover. It’s about the relation of the scale to our lived experience. Hypothetically, if you wanted to design a temperature scale around our species, you would assign the range of 0-100 to the range that would be the most frequently utilized, because those are the shortest numbers. It’s not an absolute range, but the middle of a bell curve which covers 95% of practical scenarios that people encounter. It doesn’t make any sense to start that range at some arbitrary value like 1000 or -18.

When the temperature starts to go above the human body temperature, most humans cannot survive in those environments. Thus, they would have little reason to describe such a temperature. Celsius wastes many double digit numbers between 40-100 that are rarely used. Instead, it forces you to use more negative numbers.

This winter, many days were in the 10s and 20s where I live. Using Celsius would have been marginally more inconvenient in those scenarios, which happen every winter. This is yet another benefit of Fahrenheit, it has a set of base 10 divisions that can be easily communicated, allowing for a convenient level of uncertainty when describing a temperature.