Most of my friends that still smoke will straight up tell you the only reason they do it is for the social interactions that happen while smoking. I don't think it's that different.
Regulating tobacco requires regulating the sale of a substance. Regulating facebook requires regulating speech (that is what advertising and a like button are) that happens to incite an emotional response. I'm very uncomfortable with regulating that.
So I guess it’s treated just like sugar.