Does social comparison promote self maintenance? Does the sharing of ideas lead to better cognitive hygiene? Does sharing power tools lead to less household accidents? Do we need to sniff other people's pheramones?
On a sceptical note, do extraverts, the sort of people who consent to be studied, continually arrive at conclusions that justify extraversion, missing the huge cohort of introverts who are quite content with minimal social contact?
Has a causal relationship in that direction actually been shown in research, or just correlation?
Because it seems very likely (well, certain for at least some people based on anecdotal experience) it goes in the other direction as well, i.e. someone who has serious health issues which cause them pain or low energy levels or whatever, would likely have less of a social life than if they were completely healthy even if they were the most social person imaginable before their health issues.
If for example I were diagnosed with cancer tomorrow and died of it in ten years time, I suspect it would significantly reduce the energy I have for social activity in the next ten years, but a study done just before I die finding correlation between my not having a good social life and my impending death wouldn't change the cause of death from cancer to lack of social contact.
(FYI I'm not arguing that social activity doesn't have any positive impact on physical health / length of life, in fact I'm sure that it can - I just don't know to what extent research has or hasn't shown how much it's one way or the other.)
Alcohol consumption could be something as simple as being a net positive for health in moderation after accounting for the impact of various stresses the average person encounters in life. These things are often encountered as a couple for married folks.