Who says they're neglecting them? They have a partnership set up with XDEV, they're investing into a few big Chinese games (Project EVE, potentially Black Myth Wukong), and they still "essentially" have Japan Studio in the form of Team Asobi.
Outside of that, they have support from practically every moderate-to-big Japanese publisher. I think you guys are just taking Nintendo gaining so much Japanese support with the Switch as some kind of sign Sony losing Japanese support, when it really just means Nintendo's gained a lot. There doesn't have to be a correlation. Same with Microsoft, who have (somewhat) improved relations with a few Japanese devs and pubs the past couple of years.
I think the days where practically every major Japanese AAA game being a PS exclusive, or PS just hoarding up all the Japanese development due to competitors screwing things up massively one way or another, those days aren't coming back. It's not like the PS1 or PS2 gens anymore, but that's okay. They still have a lot of things going with other Japanese devs and pubs, they're still working on exclusives with multiples of them, etc.
All the big Japanese IP that helped define PS generations ago...are still on PlayStation, and a decent number are still exclusive to it console-wise. Final Fantasy. Dragon Quest. Monster Hunter. Devil May Cry. Persona. Street Fighter. Dark Souls. The list is pretty extensive. If it's more about the quirkier Sony 1P Japanese games, well I just hope this new Spartacus service will be a means for those games to probably proliferate it. Maybe it can help make a case for a new Parappa/UmJammer, or a new Tomba, or maybe work something out with translations/fan translations of Japan-only PS1/2/3 games to go into the service officially.
Stuff that maybe wouldn't have a big retail presence on its own, but could be incentives to draw more people to the service, maybe paired with digital versions at launch or shortly afterwards.
Because most Japanese games are terrible on the tech side of things, and only cater to Japan. Sony is going for a larger, world wide approach
Then that makes cultivating relationships for more big Japanese content even more important, TBH.