Their longer lifespans likely come from better health care (especially vaccines) and better safety management (fewer pets roaming free).
The longer lifespans and poorer genetics (decreasing genetic diversity, greater inbreeding) are leading to increasing rates of cancer, allergies, immune deficiencies, etc. The poorer genetics (and greater awareness due to improving health care) are leading to increasing cases of food intolerance requiring special diets. Pet food companies are exploiting (and promoting) this increased awareness and increased rates of food intolerance to upsell owners $pecial pet foods.
There is real educational value in reading up on the nutritionally balanced raw food diets; I'm not promoting adoption of these diets. Reading up on the natural sources of the nutritional requirements is educational; how much heart muscle, liver, bone, skeletal muscle, etc. are needed to satisfy the various nutrient requirements will give you a different perspective on the use of "by-product" in pet foods.