Seems to be mainly because Bluesky is just a better user experience.
Changes in terms of service regarding AI (artificial intelligence), changes in the block feature and the presence of so many bot-like ‘impression zombie’ accounts are viewed negatively by Japanese users
But, X is still incredibly important in Japan and Bluesky isnt a serious threat to it culturally right now.
X is still a major, major news source for Japanese users, so it really won’t slow down anytime soon. Newer platforms like Threads or Bluesky really don’t have any meaningful adoption or use for brand marketing in Japan — yet
I don’t have an answer to your specific question, but honestly I think learning to subscribe to a community is a really important “tutorial” on using lemmy/reddit. Otherwise they might not understand how to get to each one. You also could just have them look at the local feed so they wouldn’t even need subscriptions.