This is purely my opinion - which I think is fair since there is no factual answer to this question yet - but as someone who lived there, the problem is the Japanese people.
Fundamentally, modern day Japanese are highly insular, risk-adverse, and too caught up in propriety and cultural norms.
As I explain it, after WWII, the leaders of Japan went all-out to rebuild the country, and by “leaders” I mean not just the government, but also the heads of business (the zaibatsu). And the best way to rebuild was to go for a strong top-down approach to running the economy. Rather than soliciting ideas from employees or encouraging participation in business or government from the workers, the goal was simply to shut up and get to work, pulling in technologies from the rest of the world and doing a better job with quality assurance, so that they had good products to sell internationally.
That allowed them to quickly rebuild and to quickly start taking over in several markets, because Japan had the newest technologies and lower failure rates in their products.
But by the point they were able to get there, the guys who were running everything were starting to get old and were either retiring or dying. And in their time in the lead, they’d trained two or three generations to sit down, shut up, and obey. They’d never developed workers nor managers who would stand up and propose grand ideas. They’d used much of the same rhetoric as the pre-WWII government, saying that everything is for Japan, rather than that business is for money.
When I was living there, around 2000, they had invented MiniDisc a decade earlier. This was a technology that was smaller and more scratch-resistant than CD, and rewritable. You could put the player in your pocket, You could split, rearrange, and merge songs - allowing editing right on that pocket-sized player. Cellphone technology was years ahead of American, with large color displays, installable apps, and multi-press keyboards. These were both huge markets that the Japanese made no real attempt to market outside the country. It just didn’t occur to them to try.
I’m sure that today, they’ve probably got a few interesting gadgets that would be big sellers internationally, but modern Japanese just don’t think in global terms. They just think about Japan and what their place is supposed to be in it.
Their school system is set up to encourage rote memorization, with no emphasis whatsoever on creative thinking, independent research, nor speaking up.
There’s a joke in Japan that the workers are “Manual People”. It varies a bit by the person, with the most extreme cases taking that title, but it’s illustrative for our purpose that the term exists and is used even by the Japanese. Basically, the best way to get promoted is through seniority and through obedience. And the best way to show obedience is to perfectly live up to the textbook definition of your job. So you end up with people working like they’ve gone through (and there may actually be) a manual describing how they are to perform their job, and they follow through those instructions like a computer program. There’s no room for creativity, personal flair, or logic. If the instructions are missing a vital step, then they’ll just lock up and be unable to do something. Living in Japan, you encounter a lot of cases where you run into some bizarre scenario where obvious and reasonable things, that would be good for business, are impossible. If it’s not in the manual, it’s just not going to happen, ever.
Fundamentally, and the part which people always ignore about economics, is that a financial stimulus exists to allow the economy to float, while the underlying problems are fixed. E.g., the housing market was overpriced and the regulations on banks were insufficient to prevent poorly structured loans, so you float the economy for a while with extra cash, so that layoffs don’t turn into more layoffs and make things worse, until the problems are fixed and market faith returns. Stimulus only works if the underlying problems are actually fixed.
If you had a group of people who are developmentally disabled and started giving them money, they’re not going to start up new companies, hire on workers, and start selling their wares across the globe. They’re just going to either buy chewing gum or squirrel away the money so that they can spend it on a trip to Hawaii when they’ve save enough. They simply don’t have the basic capabilities of acting as rational, enterprising economic actors.
Economics isn’t just math, and people tend to treat it like it is. Keynes described stimulus in psychological terms. There was an economic model to explain what would happen in the market if the psychology played out like he envisioned, just as Karl Marx had economic models for how things would play out if humans acted like he envisioned. Marx’s math never came into play because humans just don’t work like that. Keynes is closer. In the modern day US, stimulus is generally going to work, because Americans are good at thinking in terms of making money and selling things to any sucker that will take it. If you give them money, entrepreneurs will stand up and create new businesses. The Japanese aren’t like that, and it’s going to take a few generations to get over the damage that their school and career path systems are doing.
I understand where you are coming from, and I’m not trying to use the old saw analogy of comparing a household to a country, but I think that one of the large factors in what the OP is asking is Japan’s debt to GDP. If you disagree then explain why you think it’s wrong and what you think the reasons for Japan’s very long and dragging recession has been. I’m in the thread more to learn than because I think I ‘know’ the answer.