Why did victims of the black death do the dance of death before they died?

Answer 1

They didn't. The Dance of Death was an allegory for the Black Death in that everyone was included from peasants to the pope. There is the St. Vitus Dance or St. John's Dance which was something entirely different, that was more like a collective mania.

Answer 2

The dance of death was a theme in art that emerged during the Black Death in Europe. It dealt with the personification of Death, and frequently used skeletons, and other symbols and images of decay. Prior to the Black Death, most European art had focused on religious themes, depicting saints, Jesus, and other similar topics. However, during the tragedy of the Black Death, people's tastes turned more towards the macabre, and art developed to reflect the misery going on around the artists and viewers. The Plague itself became a frequent theme in art, as did the stalking figure of Death. Also, many people moved away from religion, as they lost faith since God had not saved Europe from the ravages of plague, so art moved away from religious themes somewhat.