Y"eah, the same reason we're going to have a trillionaire soon is why even if someones making a great salary, their 401k is inflating faster than they need to earn a living in a low cost of living area.
Absolutely absurd, but if you got the upswing between 2010-2020, you might be in an upper class while still living in lower class, meaning your 401k is all you need to survive on while the billionaires continue to pump the market as a defacto monetary instrument and leave the dollar for the poors.
Think of it like bitcoin, but instead of owning electronic worthless hashes, you own LLCs that own stocks and take out loans on behalf ot he LLC against those stocks.
Then you just trade those LLCs around as tokens of wealth.
Welcome to the great new oligarchy.
It's just yet another wealth transfer between classes. They can happen frequently and unpredictably, and usually but not always from workers to owners. If you happen to be in the class that benefits, you take the windfall.