The decline in cancer deaths can almost entirely be explained by the decline in smoking. Getting from 40% of people smoking to 15% was probably the biggest public health victory of the latter half of the 20th century
It's true that there has been some progress in treating most cancers and particular success in treating some specific cancers e.g. with checkpoint inhibitors. But lung cancer is both one of the most common forms of cancer (it's still third even with the massive decline in smoking) and has a much lower 5 year survival rate than the other most common cancers, breast and prostate. The massive decline in smoking has played an outsized impact on the improvement in reducing both cancer rates and deaths from cancer generally
This is true in the large sense but it obscures that 5 year survival rates have been steadily extending for many people who already have cancer. Treatments are in fact improving
