In the highly fluid U.S. corporate ecosystem, mobility is always an option. If a supplier loses a contract with Walmart, they can still pivot to another massive retailer, even if it's not quite as large.
Japan and Korea, however, have small landmasses, and the reputational risk is absolute. If a company's reputation is damaged by a single failure or a lost contract, their next job simply vanishes. Because of this existential threat, they fundamentally cannot compromise on quality. Imagine what happens to a small supplier in Japan if they are cut off by a mega-retailer like Aeon Mall. There is no backup giant waiting to take them. They are finished.
So, while geographical and structural differences dictate this extreme pursuit of quality, framing it as a "horizontal culture" is completely wrong. As an East Asian, I can confidently say that "horizontal culture" is the single most mismatched term you could possibly use to describe East Asia
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Walmart and Amazon ruthlessly squeeze their suppliers. They achieve low prices on some things and try to corner the market on others (and then raise prices). What I don't see them achieving (to the contrary, I see them failing spectacularly at) is the quality control that some Japanese companies excel at.
So there has to be something more to it than that.