So if these 40% of cancers were eliminated, what's the chances that the survivors would have ended up with one of the remaining 60%? You have to die of something. What's important is years of high-quality life, rather than merely avoiding death from any specific ailment. And of course, quality is ultimately a subjective measure. All the behaviours that you must conform to, to avoid these specific deaths, may themselv…
Eating healthy and exercising improves the quality of your life right now, as well as in the future. As does cutting back on alcohol, and smoking.
Similarly, I've never enjoyed exercise. I used to cycle to and from school every day, about 6 miles, fairly high intensity (due to my laziness, I'd start late). My aerobic capacity was certainly higher then; I could run for perhaps 30 minutes, where I'd hazard a guess that I'd be out of breath after 10 minutes now. I'm not overweight, have no difficulty walking, jumping, running, climbing hills etc. when I get the occasion to on vacation and such. But the thought of actively exercising fills me with weariness. Not enjoyable.
What I'm getting at is that I have a lifestyle that I massively enjoy, and it took a lot of experimentation and experience to discover the things I like best. Whether it is specifically healthy or not is secondary, by a long way, to how enjoyable it is.