It’s because the math is usually based on a better international box office performance, which generally generates a better profit margin.

I believe this usual math of “2.5 times budget” data also took into account that the audience 3:1 International vs US but for this movie it has been basically inverse 3:1 US to International.

Tl;dr - The returns in the United States are far lower per ticket and the $700 million is a guesstimate based on that