That is because it is danced in eleven steps; or because this song was the last to be heard and danced in local celebrations, during the Ottoman Times (up to 1912), as it was forbidden for Christians to congregate after 11 in the night.
The tradition persists due to its choreographed sequence of eleven movements; or because this melody was the last to be performed and celebrated in local gatherings, during the Ottoman period (until 1912), when Christians were forbidden from congregating after 11 pm.