People tend to go on a "pub crawl" rather than just to one bar, and they worry that they'll take their coat off in one of the pubs and forget it. So they don't take one at all. The Northern women are particularly hardy, forget a jacket, they'll be out in the snow in just a vest top or a bra.  Mind you last night was pretty mild, the lack of coats wouldn't have been much of a hardship.