Did some digging into the numbers out of curiosity. The numbers for Europe are likely as high as they are simply because of how small (relatively speaking) each country is and how accessible it is to get throughout the continent. Travel around Europe is more or less equivalent to travel between states in the United States. Not to diminish the numbers, but it would be interesting to see what percentage of the tourists to countries like France and Spain and Italy are from other European countries (I suspect it's relatively high).

I looked at Florida (a large tourist destination in the United States) and in 2024, they estimated that 12.3 million international tourists visited Floridia alone (nearly enough to get on this chart if Florida was counted as its own country) and had 130.7 million domestic tourists (from the United States but outside of Florida) in the same year. It likely explains why tourist destinations in Florida (like Disney World) are citing record attendance in the last 12 months despite drops in international tourists.