Kresley Cole and the Power of Formulas

I often here people toss around the word “formulaic” as an insult when it comes to writing. But formulaic doesn’t have to be synonymous with bad. Everywhere I go in America I can get a bucket of KFC chicken that tastes basically the same. They not only admit to having a formula, they take pride in keeping it a secret. That suggests their formula is an important part of what’s bringing all the boys to the yard.
 
So why are formulas considered bad when it comes to writing? My number one guess is...