My parents lost a lot of friends in their 40s (1980s) and 50s (1990s). Some had died in their 30s (1970s). Indeed my dad died of heart disease in his early 50s, and was hospitalised with it in his late 40s. The advice then was to give up smoking and cut saturated fats; his appetite went up and he snacked more and gained more weight.
Causes such as heart disease are better managed to reduce premature deaths and that leaves more candidates avaliable to cancers. I've recently lost 3 relatives in their 80s/ 90s where cancer is involved, but by that age range, one of the body's systems is going to be a weak link at some point anyway. It feels very different to someone in their 30s-60s with a lot of potential ahead and in otherwise good health.
While we are recognising new cancer risks, old ones have already been removed from our lives of become better managed.
Detection and treatments have improved. Diagnosis is more likely to be accurate.
DM has previously said that when she was young in the 1950s, people would sometimes just become ill, fade quite rapidly and the cause wasn't very clear. Even if it had been attributed to cancer, there wasn't the level of treatment and improved outcomes that we have in recent times.
There will be fluctuations over time with lifestyle changes, detection/ treatment protocols but we probably see a clearer picture now than in the past, and there are reductions in other causes of premature deaths.