Because life expectancy has also risen; people who used to be dying of other things are now living long enough that cancer is more common.
We live in an increasingly sleepless society and lack of sleep is effectively a carcinogen.
The present meta-analysis suggested that neither short nor long sleep duration was significantly associated with risk of cancer, although long sleep duration increased risk of with colorectal cancer.
^Matthew Walker, presumably the 70% drop is from work at his Berkeley lab
"In other words, the individual incidence of cancer deaths has actually fallen."
Situation: person has an almost undetectable cancer. They see a doctor, no cancer detected, later that week they are shot by police at a routine road stop.
We get in our time machine, go back a week and a bit, and supply the doctor with a better detection kit.
Situation 2: person has an almost undetectable cancer. They see a doctor who refers them to a specialist, cancer detected, another notch on the cancer tally board. Later that week they are shot by police at a routine road stop.
Nothing has changed except in the second case there’s another cancer detected. The person is still dead from non-cancer causes, just in one scenario they died as a haver-of-cancer and in the other they didn’t.
Better/earlier detection will necessarily lead to a decrease in cancers that are never detected (which I interpret as an increase in cancers detected before mortality from other causes), otherwise it’s not better/earlier detection.
My money is on diet and pesticides/preservatives/etc. being another big one. With this, too, there is little official evidence that, say, Roundup, causes cancer, but there is, imo, a stronger lobby against a positive outcome in those studies, and they don't necessarily control for interactions such as Roundup combined with the surfactant that it is typically mixed with that increases cell penetration.
In sum, I’d rank the risk of Roundup being carcinogenic on roughly the same level as that of 5G: possible but unlikely, given the best available evidence.
For the record, the other reasons are to do with the larger ecological impact of roundup-based practices, such as harm to soil fungi and bacteria, and collateral damage from runoff or wind. Plus, there were some studies finding it may cause harm to intestinal lining and such, even if it's not actually a carcinogen.
Pollution is lower too (again, in the US): cars used to pollute a LOT more. Smog used to be far, far worse in the LA area decades ago, so even with more people and more cars, pollution is lower, particularly localized pollution that affects people more. Of course, global warming pollution is certainly higher, but that isn't localized and shouldn't have any effect on you (it's just CO2).
Obesity is significantly worse, however.
"In other words, the individual incidence of cancer deaths has actually fallen."
Cancer rates are strongly driven by age- cancer incidence increases exponentially as people age (stochastically, of course).
I also believe many of the cancers we successfully treat would be non issues if left alone. (all the young women who found lumps and become breast cancer survivors)
"In other words, the individual incidence of cancer deaths has actually fallen."
Suppose that today the average person tells their doctor about a symptom of Example Cancer (which is incurable) six months before it kills them. 1 million people per year in Standard Country die of Example Cancer, with an average of six months between diagnosis and death.
Now, let's imagine I invent a machine, it can scan seemingly healthy people and tell them if they've got Example Cancer on average 12 months earlier. Nothing changed in terms of whether people get Example Cancer, it's still incurable, but now we've improved time between Diagnosis and Death by 200% but even scarier the incidence of Example Cancer, the number of people who know they have it, has also increased by 200%. It's an epidemic!
That machine is pretty unrealistic. A more realistic machine also gives false positives for Example Cancer. Now the number of people living with Example Cancer has increased by 500% but good news, most of those people don't die of it, because they had what medics would call "Sub-clinical incidence" meaning, sure, you had the disease but it didn't actually affect your life so who cares?