Being lazy is vaguely kinda sorta correlated with cancer… but that doesn’t account for the fact that humans who are regularly active are also less likely to make other lifestyle choices that are more significantly tied to cancer like smoking and drinking.

This is the problem with a lot of population based studies. Obesity is linked with a lot of health problems like cardiovascular disease, but only some aspects of cardiovascular disease have causative links to obesity and others are sequelae of other factors that tend to be associated with obesity. For example, extra weight/adipose puts more stress on your heart by there just being more body mass to deliver blood to and more oxygen demand from muscles to just physically move the weight around (also a cause of joint problems)… but it’s the poor diet full of cholesterol that clogs up the arteries (aka atherosclerosis) causing myocardial infarction (heart attack).