9 On October 6, 2008, the Fed started to pay interest on reserves of eligible institutions with master accounts at Federal Reserve Banks. Up to and including July 28, 2021, interest was paid on required reserves at an IORR (interest on required reserves) rate and at an IOER (interest on excess reserves) rate.
I have argued that the main reason is likely to be found in a more stable monetary policy regime in many countries. To be more precise, it might be because increased credibility of central banks has anchored inflation expectations, thereby also reducing the volatility of actual inflation. Moreover, lower trend inflation has reduced the frequency of nominal price adjustment.