I read a different article saying he wanted to try alternative methods and suggested his cancer wasn't so severe at first and was treatable, and others saying he was one of those "want to die young" type of people, so maybe he didn't care to perish early. I'm sure a better diet would've helped, cancer cells love sugar, which is why fasting and low carb diets have been effective as preventive measures, and in cases of confirmed cancer, fasting can help "starve" the cells though it may not erradicate them completely. It also depends on the type of cancer, severity, etc etc (What I Learned from Cancer)
I don't know much about Jobs, but I'm told he was more in charge of aesthetics at Apple, since my first inclination was to think "how could someone that drove technology be so against it when it came to his own treatment?" but please correct me if I'm wrong. Maybe he was more intimately involved in OS development and all of that.