it's the 70's everyone drinks and smokes to excess.
Which fandoms are you in? Yeah, I'd definitely expect more smoking then (of various kinds).
it seems many writers use it as a shortcut to actual inter character communication and relationship build up.
Yeah, I think so too, and I could certainly see this used often in shorter fics not unlike sex pollen or other tropes that basically shortcut the problems. However, I find it striking how often this takes place in longer stories as well.