because a bird never flew on one wing

The above line is generally used as an excuse for having a second pint, but evidently it can also be applied to one-day commemorative events that have suddenly become festivals. St. Patrick's Day was the first one I was aware of that made the leap from National Day of Drinking to National Week of Drinking; now I see that Bloomsday, celebrating a book which takes place in a single day, has become the Bloomsday Festival. I'm sure Jimbo would be appalled.