When Harley Quinn began unraveling all the sins in Gotham, it became clear the vigilantes around needed to look deeper than the Batman-rogues or petty criminals. White collar crime was a major issue, too. It led to Bruce Wayne eventually going to jail for tax evasion, which is why Harley is now with the Bat-family, trying to keep the city safe.
Source:https://www.cbr.com/harley-quinn-season4-wealthy-elite/