I mean, the reason why these dominate in Europe is because largely of the medieval era and a bit before that. Once gunpowder became more widely used, castles became increasingly obsolete. Nowadays they have only touristic value really or movie values, such as the castle in the movie Monty Python and the holy grail. Other than that they are just stone ruins really, some more polished than others. They have no real worth nowadays other than wonder how many resources went into building them.

Also, as others pointed out, the map is missing many castles. I also doubt the spread over China, the map only says about 7 castles in whole China? So that seems totally wrong. The definition for a castle must be incorrect, because Japan has attributed many more and that is simply objectively incorrect. Is the chinese palace classified as a castle? If not, why not? If yes then why not other palaces in China? The map is really not very good here. It should begin by a good definition of what is meant with a castle.