I mean its not like the steamdeck is flying off shelves (as far as we know) and you can play a lot of current/cros-gen games on it.
SF6, Diablo, FF, Star Wars, Hogwarts, Resident Evil, are all pretty much default playstation exclusives in Japan. We just need to be honest at this point and look at the overall software trends in japan, its not just portable or the sony platform.
The only games that stay on the charts week after week (to months) are Nintendo first party titles and Minecraft. 3rd party stuff on nintendo have the same legs as playstation games. Even some first party nintendo stuff like Bayonetta 3 or SMTV don’t do that well on the charts.
A lot of Japanese consumers are just trending more towards more casual, easy pick up and play type games. Even zelda has trended more into being more minecraft like for that very reason.
After a while you can’t really blame console manufacturers and publishers for the changing taste of one region.