It still angers me that this was Zack Snyder in 2011:
“It doesn’t. Like what Chris Nolan is doing and what I’m doing with Superman, what they’ll do with Justice League will be it’s own thing with it’s own Batman and own Superman. We’ll be over here with our movie...
And then Avengers came out.
Now MOS is littered with references to the shared universe, and Justice League is a 'sure thing' apparently.