It does obviously make a difference if the movie will make $900m, over $1bn or like $1.5bn (which it could reach if people would enjoy it more)
Not only will the costs be much bigger as the production budget but WB will obviously not get 100% of the revenue and huge movies like this are also there to get back what other movies lost. Your profitable movies don't just have to be profitable, they have to be so profitable to get all the money back you lost with other movies and have to ensure that you don't only have a black 0 at the end of the year (or even a loss)
Investors want to see as good as possible margins and not "but it was profitable, this has to be enough for you my lovely investor".
It's like saying who cares how much money Apple will make with the next iPhone as long as it will be profitable. If Apple would make 10 billion profit the next fiscal year then investors would be shocked at "how horrible the year was"
There are so many factors and to think that it doesn't make a difference to Warner if the revenue of the movie will be $500m less or not is crazy. And if it's only because the competitor is more successful with same budgets and similar movies.
There will be a lot of decisions made after this movie even if it will make some profit because it will be probably much less as WB was hoping for.
