I was just as surprised as you guys since I did expect other countries to show up here as well instead of the ones that already did but you can recheck the same on the source : https://www.google.com/amp/s/www.worldatlas.com/amp/articles/countries-that-gamble-the-most.html
Other than that US , Canada,. Japan , UK are few of the countries known for their absolute support of the crypto casinos as well.
What about your country as well ??
This must be based on a per capita basis right? Rather than total number of people gambling, as some of those countries have rather small populations in comparison to the UK and US examples that you gave. I also see that you mention certain countries give absolute support to crypto casinos as well and think this is wrong. You'll often find that most crypto casinos refuse to operate in places like the UK because of the stringent reporting and financial requirements that are often unfeasible to online crypto casinos, it's much easier for them to just block visitors from such countries no matter how rich they may be. It's not really a strong metric to aspire towards and it's kinda nice when you come down low in such results.