I think it may be the fact that he's a super perfectionist when it comes to his music. I saw his "documentary" on Disney+ and he kept rearranging the Disney songs he was supposed to perform. He literally stopped the orchestray every other minute to rearrange because he didn't like the sound
. I'm willing to bet he has plenty of unreleased songs in his repertoire but he probably doesn't like them or something. Either way, I just want something from X Japan at this point - even a single would suffice.
Dementia could explain things too though, he's getting up there in age.