I'm going to assume because those of us that actually READ comics are already established with our characters we love. And we are the base/majority of their audience and have no real interest in new characters? The next generation of comic heads outside of the movies don't read the comics where these new characters would be introduced? Just spit balling here...
Also outside of Spawn (Prior to the Black Panther movie)...is there a black super hero on par with popularity of Superman, Batman, etc? This their way to introduce this in the DC universe? Yes Spawn is Image I know...
As a black dude this "Black Batman" news made me cringe. I'm all for super heroes that I clearly identify with but just leave the clearly iconic ones alone or make it organic. Not just to fit society's screaming of wokeness the last couple years. Batman's next ward is a black kid he adopted. He's Robin for a generation of comic users. Bruce Wayne dies, next Batman is a now a black dude. Problem solved.