This makes sense at many levels -

Weight gain is a symptom of impaired metabolism, of which 96% of western adults have some degree of impairment. Most metabolism issues are driven by excessive carbohydrate load, which drives elevated blood glucose, which drives elevated insulin, which drives hormonal imbalances (i.e. weight gain).

Cancer cannot metabolize fat. Adults with impaired metabolism, with excessive carbohydrate intake, with elevated glucose levels are filling their blood stream with the very fuel cancer cells need to thrive and out compete their bodies immune system.

T2D is another 4x risk factor for cancer (i believe for the some logic as above)