> Why do you assume the long-term decline is natural and not a consequence of the various policies?
Because the long term decline predates many of the policies, I assume no causality violations.
> Where is proof for that assumption?
You're asking me to prove a negative.
Take a look at the charts here (https://www.tobaccoinaustralia.org.au/chapter-1-prevalence/1...), in the time periods covered they've banned smoking in nightclubs, shopping centers, parks, beaches, cafes, the cost of cigarettes has gone up astronomically (creating a huge black market BTW), the legal age went up, advertising was banned, plain packaging was introduced etc. During all those initiatives the decline remains pretty constant, if they were having an effect then I'd expect the decline to plateau before their introduction.
I read the link: "Hill and colleagues have suggested that the pattern of decline in smoking prevalence correlates with the level of tobacco control activities occurring at the time.11,12 The drop in male smoking rates seen in the early 1980s coincided with a period of new, well-funded media-led Quit campaigns"
There's a bunch of studies on scholar.google about the effects of anti-smoking regulation for the interested.