Everyone wants to think that where they come from is “better”. This applies to any adjectval description you can think of. I’ve heard folks boasting about the crime rates of their city in the belief that that makes them “better” (“hey, come here and we’ll show you what gang violence is like!” - “no thanks.”). Or speed limits. Or amount of graffiti. It’s ridiculous.
“Diverse” isn’t a judgement of quality any more than “purple” is. Nevertheless, if you were to get into a conversation about whose locaility is more purple, people would start boasting about levels of purpleness.
Europe is more diverse than the USA; so obviously so. That doesn’t mean it’s better; it just means that it’s more diverse. But some folks from the USA will argue until they’re blue in the face that their country is as (or more) diverse than Europe.
That’s OK, I guess. It’s been quite a while since those comparisons mattered to me, or that I felt the need to defend or prove how purple my country was compared to someone else’s.
But it isn’t a value judgement, and treating it as such tells the listener far more about you than anything about the countries in question.