Why are pink roses sacred to pink society?
This is a very very old story and it happened when they lived on their home planet, a planet full of lush vegetation with very high amounts of oxygen where life reigned, but everything has an end, the gas began to sprout from the ground and in a few years the light disappeared and all life died.
For the next 1500 years they lived in the eternal night eating the dead remains from a past world and they stopped reproducing until only one of them remained.