Because while social smoking helps in terms of meeting other smokers, it's not a big part of our social culture. Drinking (like it or not) is a huge helper socially, sure it can be a crutch in many cases, but in a whole lot of other cases its a huge boon to meeting friends and getting social.

It certainly helped me in the past, and got me through a lot of social barriers.

I'm not saying alcohol and alcoholism isn't a significant problem in many cases, but it has a well deserved social status, which I don't see as going anywhere soon. Smoking has no such status.