Sam: Can I get you something?
Austin: Do you know what bugs me?
Sam: People taking your order?
Austin: No. Taking people’s order.
Sam: Why would you do that?
Austin: Hah. You don't know my dad!
P.S: Sam works in a diner where most of the time Austin goes and drinks coffee. Sam is from a social working class while Austin comes from a very rich family. They both study at the same school. Recently Sam and Austin have been texting on the Internet without knowing each other. Actually Sam know who she is texting to but Austin doesn't know it. Austin's Dad also forces him to continue his studies at football school while Austin doesn't find it interesting and just want to accept it to please his father.
Movie: A Cinderella Story
Why did the actor use "Why would you do that" instead of "why do you do that"?