At some point they figured out that smoking is somewhat less bad for you if you smoke outside
Smoking is in no way less bad for you if done out of doors. It's because no one, not even a smoker, wants their domicile to smell like an ash tray...and when selling a house, you don't want to cut out that large swath of the population that doesn't smoke from your buyer pool.
"Smoking is in no way less bad for you if done out of doors."
That's not true. If you live in the house of someone who was formerly a heavy smoker then you have a higher cancer risk yourself, because the radiation from the cigarrettes gets into the walls and carpet. Which means that smokers themselves also have a lower cancer risk if they smoke outside for the same reason. I'd imagine it also somewhat reduces their risk for heart attack, since second hand smoke increases your risk of heart attack, although I haven't seen any stats on that.