Primarily because I don't remember the dates that coincided with the industrial revolution and mass production of cigarettes, alongside demonstrative analytics. I thought 100 years ago was a decent starting point for data.

I do remember that the first major pandemic of lung cancer started in the 1920s and the first controlled study of Cigarettes involvement with Lung cancer started in the 1950s - Hill & Doll in the US. A parallel study was started in 1951 in Britain, which ended in 2001.

Prior to that, cancer was routinely written up in case studies and submitted to journals as interesting medical cases.