I have a theory which I just came by recently which I think makes a lot of sense:

In the 1968 Democratic convention, a good number of the rank and file of the left wing of the American politics got attacked by the police, beaten, gassed, thrown in jail, sent to the hospital, or otherwise told in direct physical terms that their "allies" within the establishment weren't their friends. Before 1968, you could explain it away as one corrupt police force or local suburban society being the enemy, but maybe change was possible within the system at some level. After 1968, it was explicit: Not only are we not going to work for your goals, we might try to kill you if you try to work for your goals. Now please support us in the election, please.

It would be surprising if that led to anything other than a massive collapse in support for Democrats within the approved electoral system. It would be surprising if that led to anything other than a huge upwelling of momentum and success for the explicitly-fascist wing of American politics, that let them finally take action on their awful longstanding goals after they'd spent decade on decade losing ground.

And look, both of those things are exactly what happened. It took until 2008 until a Democratic president not named Carter held office and did anything even vaguely left-wing -- 40 years. The corporate-death project made quite a lot of progress during those unrestrained 36 years.

I have no idea if the cause and effect worked the way I describe. But it would make sense to me if it did.