It's a feedback loop - smoking was advertised as being cool way back when, which led to movie characters smoking to appear cool, which then reinforces the advertising.
When there was a push to regulate smoking in advertising, it cut the original feedback loop which made film/tv characters not use smoking as a sign of being cool. This led to advertising (if it were allowed) to be less effective at portrayal of coolness via smoking.
Vaping took off as a cool thing without a bunch of cool people vaping in movies.
People stopped smoking in movies at the same time a lot of other smoking related things changed. Similarly smokers likely notice people smoking in movies more than non smokers.
I remember a viral twitter photo of Sophie Turner smoking a Juul while filming the last episodes of Game of Thrones
Juul changed the cultural standing of vaping and (for a very brief moment of time) made it "cool" by means of social media celebrity promotion. They were hit with pretty aggressive punishment for this by the US FDA if I'm not mistaken.
Juul was founded in May 22, 2015 well after Vaping was in a fairly flat growth trajectory, and afterwards there wasn’t any kind of noticeable bump in adoption from such efforts.
It was cool to smoke when all the cool guys in the movies were smoking. One of the reasons it’s not cool anymore is that the cool guys in the movies don’t smoke nowadays (although they do it more often now than they did ten years ago; which is worrying).
Fads long predate social media. Instead social media and vaping came into their own on similar timelines but adoption of vaping just never saw the kind of hockey stick curve you see from a major fad.
Instead it was relatively slow taking ~10 years to hit 25 million users and ~20 years to hit 85 million users keeping it niche vs the ~1,100 million smokers.
It’s not that people stopped but that they didn’t start. Smoking was no longer sold as cool so kids didn’t learn of it as a cool thing.
Kids and even adults pick up cues from games, movies, books. War is like CoD and heroic war movies (why do many 18 year olds go to the army expecting glory and come back with trauma and broken dreams?), sex is like in porn, and gangs are like in GTA. Until they gain practical experience and slowly realize some things are vastly different. Maybe a couple will love “porn sex”. Most others will break a leg having shower sex and reconsider the “teachings”.
When there was a push to regulate smoking in advertising, it cut the original feedback loop which made film/tv characters not use smoking as a sign of being cool. This led to advertising (if it were allowed) to be less effective at portrayal of coolness via smoking.
It's not a simple one-to-one cause and effect.