Because for 30 years they ran an experiment where the value of Yen was kept stable without inflation nor appreciation, and that policy in recent years ended instead opting for the normal economic theory of 3% inflation making the hoarding of unaccountable wealth less desirable longterm compared to accounts and ledgers with interest rates and higher money velocity.

There is no reason they would be more desirable for becoming less stable.

Also, with the rising risk of WWIII the nation of Japan’s future is uncertain.