Because it was Mr. Sparrow who said it.

5 seconds sound clip from the Pirates of the Caribbean 1: The Curse of the Black Pearl movie soundboard.

You can hear this line at 01:46:05 in the Blu-ray version of the movie.

Quote context

[...]

- And why don't I want to be doing it?

- Oh, because... Because the HMS. Dauntless, the pride of the Royal Navy, is floating just off shore, waiting for you.

- What we doing here?

- The pirates come out, unprepared and unawares. We catch 'em in a crossfire, and send 'em down to see Old Hob.

- I know why we're here. I meant why aren't we doing, what it was... What Mr. Sparrow said we should do? With the cannons and all?

- Because it was Mr. Sparrow who said it.

- You think he wasn't telling the truth?

- Just hear me out, mate.

- You order your men to row out to the Dauntless, they do what they do best.

- Robert's your uncle...

[...]