Same thing with the removal of the gold standard. Nixon was supposed to do it temporarily but since it gave ths US the license to print money backed by nothing, why would they bring it back (they could never pay off the gold needed, there's just not enough of it mined in total). And because the US dollar is the world reserve currentcy (meaning every currency can be exchanged for a dollar) and the moment you add in the fact that banks can create money out of thin air by being able to, for example take a deposit of 100, give a loan to someone else for 80, and then there's technically 180 in circulation, however if the depositor decides to take the money back while there are no more money in the bank, the bank needs to be bailed out by the Federal Reserve, Bank of England or whatever the national bank is in this example land.