The Flash director Andy Muschietti has revealed the brutal reason why Michael Keaton's Batman retired from protecting Gotham as its Caped Crusader. Thanks to the chaos of Barry Allen (Ezra Miller) and his time-travel tampering with the multiverse, Ben Affleck's Batman was replaced by Keaton's version from the classic Tim Burton-directed movies of the early 90s. However, the tragic event that forced Keaton's Bruce Wayne into retirement was inexplicably left out of The Flash.
https://screenrant.com/the-flash-keaton-batman-retirement-backstory/