The switch to anaerobic glucose metabolism is part of the evolution of cancer as it progresses. This is because oxygen diffusion into a solid tumour is a limiting factor upon its growth. Cells which switch off aerobic metabolism will be selected for, since only they will survive and proliferate in an oxygen-free environment. You'll find this in most cancer textbooks. It's not new; I was taught this in undergraduate lectures two decades back. This switch is actually one of the key control points which holds a brake on the progression of a cancer past ~1mm in size, which is basically the limit of passive oxygen diffusion into the mass.
It's fairly logical to keep glucose levels minimal to reduce the growth of this type of tumour, and removing sugar from the diet is a simple and effective way to do so. A diet which is based upon fats will do this, since fats can be converted to the minimal levels of glucose the body needs via beta-oxidation. This will reduce the metabolites available to the tumour significantly, compared with the huge spikes you get when you absorb it directly from the gut.