That there is no one explanation is kinda why the site exists, that is the punchline as it were.

The answer you are probably looking for surrounds the fact that Nixon was just as bad a Regan.

A number of things happened in those years. Most relevant might be the energy crisis. https://en.wikipedia.org/wiki/1970s_energy_crisis

1971 saw the end of the Bretton Woods System. That was a system of fixed exchange rates between the major western currencies, that facilitated international trade. Governments guaranteed that they would exchange their own currency for US dollars, while the US guaranteed that it would exchange dollars for gold, but only at the request of other countries. In 1971, the US, under Nixon, ended that guarantee. https://en.wikipedia.org/wiki/Bretton_Woods_system

The Bretton Woods System was created toward the end of WW2 to avoid problems that plagued the world after WW1. It was extremely successful. Some cranks, aka gold bugs, argue for a gold standard. That means that the government should guarantee to sell gold at a certain fixed price. Economically, that is simply insane. These people like to point to 1971. They won’t tell you about the Bretton Woods System, though, or how that guarantee was only for foreign governments.