No neoliberalism started in full force immediately after watergate with some hints of such before it happening too. Nixon, even with his problems, was still in many ways following the old social democratic status quo of things like price controls and strict market regulation at the beginning of his presidency. The neoliberal experiment really began with Penochet in Chile as well which also happened in 1973.

The primary reason neoliberalism resulted in the productivity wage curve shifting is that prior to this, large enterprises weren't nearly as much of a thing. Smaller employers had to pay their workers more since hiring was harder, domestic manufacturers didn't have the ability to outsource in the same way due to lack of standardized rules of trade and exchange rates so unions were also able to thrive,

The rise of large global enterprises resulted in highly optimized supply chains, you had far less "duplicated" work within the world market, later on came automation and we ended up where we are now. It's worth pointing out that the productivity wage curve never actually dropped out for those in the top 20-30 percent of income, which is a primary driver of middle income wealth inequality today, but it is this group that both automated, optimized these supply chains, fired a bunch of domestic workers and busted their unions.