Not sure if it makes sense to try to pin it down to a specific year or even one specific “thing” that happened, but there was a massive anti-antitrust (so “pro-monopoly”) movement that started in the early 1970s and really took off under Robert Bork:

https://en.m.wikipedia.org/wiki/Robert_Bork

Corporate raiders came along in the 80s and started gutting everything a company did that wasn’t purely maximizing shareholder value. Any publicly traded company that resisted got a hostile takeover (not really a common thing before then). Followed by fifty years of judges “learning” that every corporate action that someone can claim will lower consumer prices is to be allowed (whether the claim actually comes to pass or not).

I recommend Robert Reich’s online class about wealth and poverty. It lays out a lot of interesting concepts.

https://youtu.be/1f2blKai7HA

Also Elizabeth Warren pointed out in “the coming collapse of the middle class” that in the 70s companies realized they could feed the expectation of improving quality of life by withholding raises but offering unsecured credit in the form of credit cards.

https://youtu.be/akVL7QY0S8A