But they can't sell more widgets if nobody has any money to buy them.

Sure, you could model a pretend economy where only the wealthy ever buy stuff, but that's not how the US economy works, and Consumer Confidence has a massive influence over our GDP - so when our GDP goes up, it's often hand in hand with our population buying more widgets with extra money, even as they complain that they don't have the cash for "necessities" (I.E. burrito taxis, vanity pickup trucks, and owning a house with two spare bedrooms with a <30 minute commute to their workplace).

Note: I'm not saying that low-income Americans don't genuinely struggle, just that there's a mismatch between the Americans that are genuinely low-income and the Americans that perceive themselves as low-income because they need to save a little to make major purchases or need to tell themselves no sometimes.

> you could model a pretend economy where only the wealthy ever buy stuff

In the United States, the top 10% of income-earning households are responsible for approximately 50% of all consumer spending.

And yet we see all of these better outcomes on metrics more directly tied to human flourishing in countries that have worse per-capita GDPs.