Because it makes you smarter:
(Source Marginal Revolution)
Note: I am joking, this is not causality. For one we don’t have a quantity measure of drinking, and the impact of drinking on intelligence is no doubt non-linear. In fact, you could make the argument that “smarter” people know how control their own alcohol consumption, and so do not face the severe negative impacts of drinking – in a way smart people are more likely to find ways to control, or are not subject to, time inconsistency problems in liqour.
However, I think we should also use this as a reminder that it the link between the consumption of a drug and the drugs impact can be very poorly estimated if we aren’t very careful to control for these sorts of issues – hence why I do not trust a lot of studies out there, especially the ones made by interest groups where all they do is draw lines (95% of studies according to my casual observation).
Update: CPW sent me the link to the full set of graphs with alcohol involved – it is beautiful.