0°F is shorts weather for some

Only for those with medical issues or those being obstinate. It's not a relevant data point when trying to agree on a scale. 99.9% of people will agree 0F = cold as fuck.

There are hundreds of millions of people who see negative double digits every year

So? The difference between 0F and -10F and -25F aren't THAT significant. The VAST majority of people will treat those temperatures as similar unless they're preparing for an outdoor adventure or something. But the difference between 65 and 75 is HUGE to most people that WILL impact how they prepare for interacting with the environment.

For daily use all temperature scales are arbitrary. Why not use one that’s useful?

This is just not accurate and is pure cope. A scale that's 0-100 for the most important temperatures that humans interact with is an objectively good scale. With 10 degree bands that align pretty well to general human comfort and indicate the type of preparation required. Sure, some people might consider 60s t-shirt weather, but the point is the band is still relevant. 60-70, 70-80, 80-90. Those are useful, meaningful temperature ranges where the temperature inside those bands is similar enough