401k isn't necessarily dependant on the stock market, but the stock market being the 'right' investment has been a self-fulfilling property, any 'default' election goes mostly stock, because stock goes up. stock goes up in part because a portion of everyone's paycheck defaults to being spent on stocks.
But what you can do with a 401k can be limited. I was looking at my options for something that would be a bit more bubble resistant, back testing them against the crash of the attack on Iran, and every single one of the options my plan allows had market exposure, even if more of them were not directly stock.
Well, since they are using GenAI, someone is litterally getting paid by the word...