Why was prophet Lot (pbh) told not to look back?

> "Then travel in a part of the night with your family, and you go behind them in the rear, and **let no one among you look back**, but go on to where you are ordered." (Qur'an 15:65 ) Why was Lot (PBUH) told not to look back when the angels were destroying Sodom and Gomorrah? Why was it so important not to look back?