See,the thing is you have to truly understand world building.
The movie was beloved by critics and fans. It bought you the smash hit "Peacemaker"
"The series, which is a spinoff of last year's "The Suicide Squad" and was created by the movie's director James Gunn, was the most in-demand original streaming TV series in the world as of January 22, according to the data firm Parrot Analytics. It was 69.5 times more in demand than the average series. "
Plus im sure characters like RatCatcher 2 could get a series or make future appearances.
It made D.C realize they needed to steal Gunn from Marvel by offering him the entire DC universe. Here we are today and Superman is a resounding success on all fronts. And a succesful Superman means we officially have a DCU for the first time. Because without Superman there can be no DCU

. Glad i was able to add clarity