The main reason for the PS5 and PS4's console and software's poorer performance in Japan is Sony themselves, they just realize the biggest market is the western one, and just like Microsoft have gotten into bed with all the major western development studios, even it's first party development teams are from these regions.
Japan has now become a mobile game market now and of course Nintendo and t'ts most successful consoles fit right into this template, also the Japanese like to support their own development studios and games, and even mega hits like Grand theft auto fail to sell massive numbers in the region, I don't thing it's down to the maturity of the title as Japanese studios do make more mature themed games as well, it's just he Japanese buying public just like to support Japanese consoles and games.
Nintendo are pretty much a perfect fit for this market as most of their top selling games are either first party or from Japanese developers.