Because sugar is addictive but fat isn't. It's harder to make money by selling fat.

I didn't know about Yudkin. I did read Atkins book and it convinced me that sugar was the real change in our diet and the cause for obesity. I went on his plan, lost 40 pounds in a year and have been able to pretty much maintain a fairly consistent weight since then. I cut out as much sugar and cheap carbs as possible. I eat pretty balanced, not total non-carb. Every year I'll go on a month of salads to recalibrate.