I would be a little careful with insinuating that USA had some “Good Old Days”. Prior to WW2, most Americans lived closed to subsistence lives — and there was a fair degree of apathy, cynicism, and distrust back then.
After WW2, there as a unique economic opportunity for USA. With its western system of governance and a less damaged infrastructure, this nation was poised to be the world leader. This dovetailed into the labor movement getting more than its usual share of influence. The middle class got bigger and social-economic mobility was more possible.
But there really hasn’t been a strong middle class in history. Humanity’s natural tendency is about the Orwellian 2% elites, 13% middle class, and 85% proletariat. In other words, the western social structure post-1945 is an aberration of history.
Some things seem to suggest we westerners are going back to this arrangement. But I’m not so sure.