There should be some in-built bias, such as adding points for just being in the Northern America. Otherwise it's hard to explain how all of the diverse cities of the USA end up being clumped in one place of the scale. That, or not having sufficient dynamic range.
Have you perhaps considered that they're not very diverse? NYC and SF are a bit different yeah, but other than that they're all remarkably similar. Honestly it's a significant factor in why I decided to move back to Europe. It always bothered me when Americans claim that the US states are as diverse as separate countries in e.g. Europe. No, just no. You are blinded by the fact you've grown up there and are attuned to the small regional differences. There are as large regional differences within individual European countries as there are in the US.