They pay you in reputation, and reputation doesn’t transfer to other big corps since they see frequent job changes (sometimes capped at twice in a lifetime) as a red flag and won’t hire people.
Due to the more or less deflationary economy, Japanese wages have not increased for the better part of three decades. (Deflating prices mean that even with stagnant wages, you're still able to buy more.) Job hopping is unlikely to actually result in increased wages. (Inflation is now coming to Japan due to the general global inflation from the war in Ukraine, so that will be an interesting scenario to watch.)
Japan is a heavily reputation based society. In the way that US uses credit score to determine a lot of things, Japan uses this sort of reputation as a proxy to determine eligibility for many things. As a general example, finding in apartment in Japan requires a guarantor (essentially a cosigner who agrees to act as a fallback option in case you can't pay) and landlords want a Japanese national person or entity to do it most of the time. https://blog.gaijinpot.com/what-is-a-rental-guarantor/
Reputation is also highly correlated with company stability in Japan.
Such reputation buys you things like A) easier time attracting a future spouse B) respect in certain social circles and transactions, transferrable to your partner and children (yes this is a thing) C) a network of individuals also “smart and hardworking” like you
