Apparently, in these modern times most people tend to fornicate during the holiday season. Condom companies claim that their sales peak around Christmas, long weekends such as Memorial/Labor day and (oddly) Mother's day. Before the introduction of holidays, natural things like "light" and "weather" would affect copulation. Now we're so tuned into work and social lives that these annual reprieves have become both holidays and HOlidays...(get it?) Instead of feeling moved toward intimacy, couples feel forced or obligated because it is a "special" time of year.
So in 20 years when the next batch of kids is coming to fruition and they ask their parents about the occasion of their conception, they'll be pleased to know that their entire existence is based on Mom and Dad forcing a "'tis the season" quickie between strip malls on Black Friday.