The way these event/themed sales work is that Valve informs developers about them a couple of months in advance and then developers have to submit their games to be included. There's minimal curation from Valve's end. For example, here's the announcement for the Halloween sale where they say that 'spooky' games in particular will be surfaced but developers of other games are also free to participate. If games from Japan aren't appearing in these event sales then it means that the developers have not submitted them for participation. There could be any number of reasons this happens including not wanting to devalue your games, focusing on more traditional sale events like Golden Week, maybe just not seeing the value of these themed promotions, or most likely (in my opinion), just being oblivious to them.Same sort of situation with Visual Novel Festival. Barely any Japanese-produced titles were featured. Typical Valve.