I think you will find that dog (pet) importation is more highly correlated with higher income, thus while the highest population countries are listed, in % wise, higher migration will be from Europe.

In outside the covid pandemic, I think you will find that there is significant international travel for breeding and show purposes. Additionally, while I am unsure of the cost in the US, in a place like Australia the quarantine costs to bring pets into the country make it something more likely to be done by wealthier migrants.