They literally were defaults. The reason for Bretton Woods, and the reason the USD became the overwhelming world reserve currency, is that it was directly convertible to gold. Buying USD was as good as buying gold, which meant the currency was not dependent on any given country.
But then due to poor economic policy we found ourselves in a situation where we had far more issued debt (currency) than we had gold. We were forced to default on those debts, withdraw from Bretton Woods, and basically just told the rest of the world 'deal with it.' A famous quote from the Secretary of the Treasury at the time was, "The dollar is our currency, but it's your problem."
You say we left Bretton Wood due to "poor economic policy". If that were true the economy of the US has performed poorly since 1972. That's crazy. Worse, it implies that we should go back to the gold standard. That's also tin foil hat proposition.
A default is by definition when you break a contract. On July 1944, the US signed the Bretton Woods Agreement. Agreements between countries change, they aren't contracts. That is why I don't think it is literally a default. Also, history has shown it was a sensible and beneficial thing to do.
I'm not going to debate semantics, but I will hit on the other issue. This is a site you may find interesting: https://wtfhappenedin1971.com/
The reason we were forced to default (or whatever you want to call it) on our obligations under Bretton Woods is that our economic policies were enabling inflation to start spiraling out of control. Cumulative inflation from 1913 to 1970 increased 306%. That was a major problem. From 1913 to today? It's 3091%. This causes countless problems in society. Take wealth inequality for instance. Workers have always expected annual raises, even in times of negligible inflation, but in inflationary times those those raises often struggle to even keep up with inflation. This [1] is a graph of real wage for workers. It understates the picture as it starts in 1979, at which point the decline was already in full swing.
But even there, you see but a 10% real increase in wages over the past 40 years. By contrast, real GDP/capita [2] has increased by more than 100%. And not only are there are far more basic costs to life today than in 1979 (internet, electronic devices, etc) but many things like housing and education costs have accelerated dramatically far ahead of nominal inflation. So you have a world with more billionaires than ever, and one where more people than ever can't afford to even feed themselves without government assistance. And this is not even scratching the surface of the issues. Basically we had a small problem in 1971. Instead of solving it, we stuck a bandage on it - leaving a later generation to solve a dramatically larger problem.
But then due to poor economic policy we found ourselves in a situation where we had far more issued debt (currency) than we had gold. We were forced to default on those debts, withdraw from Bretton Woods, and basically just told the rest of the world 'deal with it.' A famous quote from the Secretary of the Treasury at the time was, "The dollar is our currency, but it's your problem."