It got sad because enough folks across enough strata aren't doing well in enough ways that matter, and yet are constantly told that the numbers/statistics/data tell the opposite so clearly they're in the wrong.

Just look through the comments here for more evidence of that sentiment: for every commenter saying they did everything right but can't afford a home, there's someone else storming in with cherry-picked data showing that ahkshually homeownership for younger cohorts is getting better so obviously it's a problem unique to you and not the larger demographic. For every commenter complaining about wages not keeping pace with inflation, there's another commenter barging in with ahkshually the basket of goods indicator suggests you're wrong and everything has never been more affordable, so it must be a you problem.

America is so sad because we keep saying "we're having problems and need help," and the response is consistently along the lines of "Ahkshually everything on this graph is great and we're not going to look any deeper than that so it must be something you've done to deserve this." Nobody is listening to the meat of the grievance, just immediately punching down on the aggrieved. That makes us sad.

As for the "u rich why so sad" argument? Because you're conflating the wealth of the whole for the wealth (or lack thereof) of the components. Taken as a whole, America is fabulously wealthy; hell, taken individually, Americans earn and are worth more than any other society on the planet, period. Yet when you start boiling down to individual pictures, it becomes clear that the wealth of the country is intensely concentrated in fewer hands, and that those hands have no intention of ceding that wealth to the government nor using it to govern effectively. The problem isn't wealth so much as wealth inequality, and just mentioning that phrase is going to get this downvoted into oblivion because the last thing a country of pretend-billionaires wants to admit is that they won't actually be wealthy themselves someday.

EDIT: One little nugget I've been chewing on lately with regards to this whole thing is that perhaps the financialization of everything is a contributing factor. Before computers spat out "optimized" pricing for every good, service, and transaction out there in the name of maximizing profit via "objective" measures of value, human elements could choose to eschew that in favor of prioritizing other outcomes - like cutting tenants a break on rent when they got laid off so your building had a stable set of known inhabitants that were more predictable and invested in the community, for instance, or paying workers more and investing in their training so they wouldn't be tempted to leave. By optimizing for profit, we removed humanity from a very human system; by worshiping entities like "the invisible hand of the free market" and "efficient distribution of resources via Capital allocation" as if they were gods, we hand-waved away any obligation of those with outsized success to provide support for those who failed to achieve it themselves.

That would explain the vast chasm between the "mood" and the "stats", in a way: the system might be optimized for maximum profit, but it has come at the expense of prioritizing a healthy human society, and the humans are feeling that more and more.

As for all the talk about how humans are ultimately the ones making these decisions - are they, though? Are they really? Because it doesn't look like the C-Suite and Boardrooms and investor classes out there seem willing to sacrifice some profits for improved human conditions; the consistent pattern continues to be along the lines of "the computer said X", and that's the extent of the discussion lest a human risk being accountable for that decision.