That surplus income is only surplus until you have medical event, catastrophic loss, or need a major repair (roof). Ot to mention the need to save for retirement. It's those extraordinary living expenses that kneecap you.
Re:How to Work Hard
by joshuamorton on Tuesday June 29, 2021 @01:01PM
(#27678641)
Whiler I agree with the thrust of your comment, your committing an error: the distribution of incomes isn't uniform across time/age. That is, the set of under 30 and under 40 household with 12k/ year is lower than 40%. If you look at not the median household at this moment, but the lifecycle of the median household from when it started to when, it probably couldn't save 10k/yr until recently.
And the early years are the most important ones.
Americans are notoriously poor savers, also per the US government, but a large percentage of all households -- at least 40% -- could fairly easily accumulate $1M if they were diligent about saving and investing a decent fraction of that surplus income. The surplus income is available but Americans choose to use that income for things other than saving and investing.