The increase is cancers in younger age groups was noticed earlier than that, and the cancers can't be expected to occur instantly upon exposure to a carcinogen.
Many people instinctively attribute this rise in colon cancer to diet products, almost pretending as if it is the only thing that has meaningfully changed over the past 40 years or so. Others like to point to changing consumption habits in people drinking more sugary beverages.
It is almost as if everyone is projecting their personal believes into this. But the truth seems frustratingly simple: we really just do not know yet
Probably from your inability to read what I actually wrote. The word "suspicion" does not connote confidence.