Why were American accents common?

Question

In Total Recall (2012), most of the world was rendered uninhabitable. Two regions remain habitable, the UK and Australia. So you'd expect accents appropriate to those areas to be common. However, in the film, almost everyone has American accents. I would normally brush this off as a result of it being a Hollywood film, but one of the exceptions hints there may be more to this.

When Lori (Kate Beckinsale's character) reveals herself to be an undercover cop, she switches from having an American accent to having an English accent. The English accent then persists through the end of the film. This implies that to be a convincing wife to Douglas, she needed to have an American accent, so there's some in-universe importance of accents.

So my question is, why were American accents so common, instead of UK and Australian accents?

Answer 1

Quoting from a Hearld Sun (Australian newspaper) interview with Kate Beckinsale:

When you go bad in Total Recall, your accent changes from American to English. Are British people more evil?

It's mandatory for British actors to play a villain in an American movie; that's the law. Other than that, the fact she flips into her English accent adds a sinister, "Oh my God, you've been lying this whole time." -- Kate Beckinsale

Aside from that exception, it seems like they were just following Hollywood's usual playbook.

Answer 2

The American accent is a BLEND of all the other accents of all the people who settled there.. If only tho UK and Australia were left inhabitable, naturally ALL refugees would end up there, and the local accent there would also become a blend that SOUNDED like an American accent. One version of an American accent anyway, seeing as there are so many to choose from.