Why did the mother agree to go out for dinner?

M: Mum, what will we have for dinner?
W: Maybe fish and chicken soup. What do you want to eat?
M: Why don’t we eat out?
W: That’s a good idea. Actually I’m very tired today.
M: What about KFC this time?
W: OK, then, you’ll drive, won’t you?
M: No problem.
  …
M: Mum, here we are. What would you like to have? I’d like a hamburger.
W: I want one, too. And some desserts and beverages?
M: Yeah, a glass of Pepsi, an ice-cream cone and an apple pie.
W: OK, you go and find the seats first.