You realize rarity is referencing the relative percentage of an event or item and not the absolute number right? If you have 1 million people in the numerator, but 100 million in the denominator, then the rate is pretty rare

On a planetary scale, I wouldn't actually consider that 'pretty fucking big'. For comparison (metro areas, figures from Wikipedia):

San Francisco: 4.7 million

Berlin: 6.1 million

London: 14.3 million

NYC: 20.1 million

Shenzhen: 23.3 million

Tokyo: 37.5 million

I never realized how big Tokyo is. Wow.

In fairness, it was a bit unfair to include that one, as Tokyo is the biggest city in the world!

https://en.wikipedia.org/wiki/List_of_largest_cities#List