Currencies are highly fungible. The dollar is shitty, but it still beats all of the alternatives. Any country could swap their dollars for any other currency, more or less at any time. So we must come to the conclusion that countries keep (and accumulate!) dollars as reserves because they prefer it.
Yep he stopped the gold standard because of inflation and he knew investors
Fixed that for ya. The closing of the gold window was Nixon's solution to the Triffin dilemma. Well, maybe not solution exactly, but at least an attempt.
The era after the close of the international gold window is known as Bretton Woods II, or the Washington Consensus.