> despite there being at the time almost zero evidence for
This isn't true—people had been connecting the dots for a few decades by the time these ads were running [0], and right around the start of the run (1940) was when strong evidence was starting to get published:
> Scholars started noting the parallel rise in cigarette consumption and lung cancer, and by the 1930s had begun to investigate this relationship using the methods of case-control epidemiology. Franz Hermann Müller at Cologne Hospital in 1939 published the first such study, comparing 86 lung cancer ‘cases’ and a similar number of cancer-free controls. Müller was able to show that people with lung cancer were far more likely than non-cancer controls to have smoked, a fact confirmed by Eberhard Schairer and Eric Schöniger at the University of Jena in an even more ambitious study from 1943. These German results were subsequently verified and amplified by UK and American scholars: in 1950 alone, five separate epidemiological studies were published, including papers by Ernst Wynder and Evarts Graham in the USA and Richard Doll and A Bradford Hill in England. All confirmed this growing suspicion, that smokers of cigarettes were far more likely to contract lung cancer than non-smokers.
So it's less a case of people intuiting what was bad for them and more a case of the industry trying (and for a few decades succeeding) to get ahead of a growing scientific consensus by advertising it into irrelevance.
[0] https://tobaccocontrol.bmj.com/content/21/2/87