
Continuity mistake: When they are looking at prospective husbands, Princess Mia and Lilly are eating popcorn and Lilly asks if it tastes like pears. Princess Mia answers its a "Genovian specialty," and the popcorn disappears immediately afterwards. (00:25:45)
Answer: My guess is because Mia and Michael didn't actually start dating until the third Princess Diaries book. The second and third books were all about Mia trying to get Michael to go out with her, and since they went out at the end of the first movie, they couldn't base the second movie on the second book.