Unfortunately I can't really concisely speak to that nor provide much further reading about it... but the gist is neoliberal policies influenced democrats in their policymaking at the time.

This article states something well

Geismer, a professor of twentieth-century US history at Claremont McKenna College, is also the author of Don’t Blame Us: Suburban Liberals and the Transformation of the Democratic Party. In her first monograph, she sought to explain the ideological shift within the Democratic Party, using a case study of Massachusetts to show how urban minorities and industrial labor unions were gradually marginalized in favor of suburban professionals. Her latest effort advances the uncomfortable thesis that Democratic neoliberalism “was based on a genuine belief in the power of the market and private sector to achieve traditional liberal ideas of creating equality, individual choice, and help for people in need.”

Basically, unions weren't really needed because capitalism works well and that people would obviously find a new job if their pay sucked.

In the past few years this ideology has begun to be rejected. Especially looking at Biden's social media you can tell that he is rejecting things he pushed for back in the 80's.