I’m a cyclist, mt. biker, and motorcyclist and with a couple of decades of road riding under my belt can, with a considerable degree of authority, say that most roadies are complete and utter tw@ts. I don’t know why single file, especially on a narrow and busy road, is such a difficult concept.
They believe they’re making a point by blocking the road for evil motor vehicles, it’s intentional and it’s political. The same motivation has them doing it during commuting hours.