Why didn't Katie Holmes play Rachel Dawes in The Dark Knight?

Question

Katie Holmes played Rachel Dawes in Batman Begins but Maggie Gyllenhall played the character in The Dark Knight.

Was there any particular reason why Katie Holmes didn't continue on in the role?

Answer 1

According to Julie Polkes, a spokeswoman for Ms. Holmes,

"Katie was offered but was unable to accept the role because of scheduling conflicts. She was in the process of negotiating for another project. In addition, when she returns to work, she would like to tackle a new character."

But according to this article,

The studio is searching for a new actress who can replace Ms. Holmes in the big-budget picture, for which the salary range likely would have been $1 million to $2 million, say these people, compared to the roughly $1 million she earned for "Batman Begins."

Answer 2

No one can ever know if her public statements were the real reason(s), but she supposedly turned down coming back so that she could be in "Mad Money".

See this MTV article.

"Not at all. I had a great experience working with Chris Nolan [and] I'm sure it's going to be a great movie. [But] I chose to do this movie ['Mad Money'], and I'm really proud of it," she told MTV News.