My guess would be that it's related to the UK's "no fun allowed" Online Safety Act, which goes into full effect this summer

It applies to any large-ish "platform" that serves UK users, and they're trying to bully the entire world into kowtowing to it. Perhaps those Japanese services decided to just shut down instead of receiving a fine or geoblocking the UK - especially since their services have likely been mostly dead for the past 15 years

Sage for serious business