Actually, in 1933 the US ended the use of the gold standard, following the UK (well, British Empire) which abandoned it in 1931.
What came to an end in 1970 was the Bretton-Woods system where global currencies were pegged against the dollar. There was political control over the tax rate between 1946 and 1971, but the US was always able to unilaterally end the system. It did so to print money to fund the Vietnam war (sort of).
The peg against the dollar meant america could have $100 of stuff from the UK or France by printing it, whereas we needed to pony up actual goods and services. It wasn't ideal.
The system was also put under pressure by petrodollars. Western purchases of oil were a leak of the currency outside of the Bretton Woods countries. Since Bretton Woods was ultimately about governments being able to regulate their currencies, petrodollars weakened their grasp and created markets which threatened confidence in the system.
The 1980s are where the real issues began, because most countries moved to fractional reserve banking rather than full reserve. The risks this produced in the system caused the 2008 crisis and led to the epic price inflation in housing etc we have seen in the last forty years. QE is an admission of defeat of the system introduced in the 80s, a hope that eventually we can go back to that time. No interest group has been strong enough to properly challenge this system, so it has yet to die.
TL;DR it ain't about gold, it is about banks
Edit: removed errant hyphens in "Bretton Woods".