Japan has a way stronger economy than most unstable "developing" shitholes. Its currency was stronger than those of resource exporting ex-Soviet countries. The monetary policy is to artificially weaken it, also giving enough breathing space for the monetary intervention in case it gets out of control. Despite poor inflation \ economic expansion numbers throughout the years, there is still a lot of activity, a lot of consumption happenning. Levels of poverty are extremely low compared to that of China and South-East Asia. On top of that, there is no inter-ethnic or inter-faith strife, with political instability risks low.
Compare that with a country like, idk, Uzbekistan. Shit currency, shit government, shit economy. The government is run by ex-CPSU or ex-KGB, while the population is still drenched in poverty after a century of communist tyranny. The economy is still in the hands of the state, with slave labor being used to pick cotton to be sold to Bangladesh and Indonesia for textile manufacturing. On top of that, climate is shit - I was just reading headlines that people are freezing there, and the heating oil is skyrocketing price-wise. Bad infrastructure adds insult to injury. Nobody will invest there. Their government bonds are CRAP and the national currency dropping double digits throughout years. Oh and that's just the start. There's also Afghanistan just to the south and it's full of islamic extremists trying to topple the government since the early 1990s. etc. etc. There are so many basket cases in Asia, Japan is not it. Yes, it sucks by the U.S. standards, but most of the world economy is just abysmal compared to the U.S. Japan is still in the top 5, and it will take a while for the 1970s-1980s economic boom legacy to expire.
You want to see a true puzzle look at Argentina. Japan is doing great. Argentina has been in a perpetual economic crisis since the 1940s wartime embargo, imposed on it by FDR for refusing to declare war on Germany. Not a single decade of relative stability since. Some may argue that it started even earlier in 1930 after the new government took power following the U.S. stock market crash. It's been a non-stop shitshow with coups d'etat, silly wars with Britain, threatening Brazil (lmao) and Chile with wars, currency crises, and the curse of Juan Peron's retarded policies haunting the country's political life to this day.