Correct me if I'm wrong, but that seems like a gold bug website, advocating for "hard" money (e.g. gold or bitcoin). I'm pretty sure the answer they want you to find is that in 1971 the US ended convertibility of the dollar to gold: https://en.wikipedia.org/wiki/Bretton_Woods_system. It's actually a pretty clever persuasive trick (ask a question designed to lead someone down a specific research path and "self-discover" your true message (a trick thats's coincidentally also used by QAnon: https://www.axios.com/qanon-video-game-cbbacb1e-969c-4f07-93...).
However, the argument of those graphs is pretty much correlation = causation. I'm not economist or historian, but I do know that a lot was going on starting in the 70s (recession followed by the rise of neoliberal economics, among others), that may offer a better causal explanation than gold.
https://wtfhappenedin1971.com/