It doesn’t help that DC has lost its appeal in the last decade or so. Marvel has had a bumpy 4 years, but DC has really lost it in the past decade cinematically aside from Joker 1 and The Batman, the comics have been INCREDIBLY hit or miss, and their games have been pretty awful too. They excel with their animated shows, but that isn’t where most new fans are going to come from anymore.
Superman, Batman, Joker, Harley Quinn, Wonder Woman, and Flash will always have staying power as IPs, but there’ll come a point where they either need to theme to characters nobody currently cares about, or just stop theming to DC. Personally I hope it’s the latter, but time will tell.