> Why did everyone across the entire political spectrum abandon individualism in the 20-teens?”

You mean in the aftermath of the great recession where most people were struggling economically and saw that the rules are only for little people? The 20-teens were the time of Occupy Wall Street and the Tea Party - I don't see how it can be

I think individualism increased, after the teens, in a "don't trust the experts, do your own 'research'" way. Regardless of one's politics, its hard not to be a conspiracy theorist when you see a conspiracy play out in front of your eyes, at your expense. You could draw a straight line between the GFC and the growth of the "burn it all down" contingents on the left and right - indeed, a lot of "Bernie bros" became Trumpers whole remaining true to that ethos.