Memes

Generally I think it's because the Japanese have had continuous cultural interacting with the West for centuries at this point. Everything from Dutch and Portuguese trade during the sengoku jidai, to pirate ronin in the Philippines during isolation, to Japanese communities from Baja Sur to the cascades, and then finally stable connections being made post commodore Perry. In contrast the Chinese have had less than stable connections due to massive cultural changes every couple hundred years including periods of isolation, the collapse of the Ming fucking up trade routes for a time, the Qing being notably more isolationist, the warlord and Republican period being a shitshow, followed by the isolation of the communist period shattering a lot of western interst, it makes for less than stable connections.

Also there's the whole great firewall of China thing going on which further seperates things in the modern age of the internet, it's not total separation but it's enough to be notable. In contrast I have been cussed out by a Japanese person, a Ruskie, an Aussie, and a fucken Peruvian simultaneously while playing games.