Why would a book be set in London, England?

i have to state the significance of this setting to a quotee,



the book is Remember Me, by Sophie Kinsella.





If you haven't read it, it's about a girl who wakes up in a hospital 3 years later in her life. She thinks it's 2004, when it's really 2007. She suffers from amnesia %26amp; goes from being a middle class, "ugly" girl to a beautiful rich girl, who has a perfect life. She has a difficult job, a beautiful, wealthy husband and a perfect house.



What could the significance using London be in the story?Why would a book be set in London, England?
It could have been the author's or a relative or friend's hometown or birthplace.