I have read a lot of books (mostly non-fiction) that I would not classify as creative, but was still a best seller. I have also read non-fiction that was downright bad, but through the power of PR became a best seller.
I will however concede the point that being creative in your writing will make it better regardless if it ever makes it to the best seller list.
Anyone that writes wants a best seller, but they should want to make sure they produce quality work that will be discussed, debated, and used even if it never makes the best seller list. While my banker may tell you he wants me to write the best seller my own goal is to produce quality work, which I hope is appreciated by the world and becomes a best seller, but as anyone that has seen bad work hit the best seller list can tell you tis not always true.