As a child growing up in Canada, I don't recall reading many books about characters that weren't white, which seems unusual for a multicultural country. In fact, when considering many of the books I've read over the years - including bestsellers - I believe the majority featured mainly Caucasian characters. Interesting.
Now, I go out of my way to both read and write books with diversity because it's important. Why is it important? Well because it's realistic. That's our world. Why do we need it now more than ever? Turn on the news and you might get an idea. Governments and narrow-minded groups are attempting to divide us but the beauty of books, movies, and television is that we have the ability to bring us together and show that we really aren't so different after all.
And that's why diversity matters. I challenge other writers to include it in their books.