I think flop is a poor choice of word that kinda detracts from the point OP is making. Sales are lacklustre in NA it seems, especially when compared to EU and other racing games in NA
There are no other racing games to compare, though. Actually, nothing can be compared as we only have placements.
For arguments sake, we can just guess that US sales are exceptionally better than UK since the games are cheaper there, and there us no region locking. Everybody in Croatia purchases their digital games from the US store, as you can save up to 20€ per game.
So the UK numbers, even though #1, might actually be a complete flop, while placing #5 in the US turns out to be a huge success.
OP is just stirring the pot because he is bored, there is nothing of value here except assumptions and speculation.