Coinpot adjusts its claim rates based on your location, and no the highest claim rate isn't just in the US. They work in the same way as this site, They have countries classified into several classes or tiers (ignore the multiplier in the pic since I don't know how exactly coinpot calculate their claim rates), so Countries in Tier 1 have the highest claim rates (You can check that yourself by using a VPN and you will see that they will show you equal claim rates 
), Countries in tier 2 get lower claim rates and so on.
Again, ignore the multiplier, since this pic is from another site that follows the same concept, Hope that helps clear the confusion abit
https://i.imgur.com/aIIMm4P.png
But why? I'm sad and angry in one time, they treat me like tier 2, in a decentralised society where cryptocurrency is equal for everyone no matter where are you from. ), Countries in tier 2 get lower claim rates and so on.Again, ignore the multiplier, since this pic is from another site that follows the same concept, Hope that helps clear the confusion abit
https://i.imgur.com/aIIMm4P.png
Yeah it is sad, but they seem to be arranging it based on popularity of countries or how strong/developed they are, I don't know the right word but yeah. It's just how they do it and I guess they do this cuz it saves them some bucks in the process (or maybe they think it is fair, like you live in Egypt so you earn pennies, X lives in the US for example so X gets higher etc)