As she was the goddess of love. Cosmos knew that nothing brought families together like children. Children were the true bond that held partners together for life. And children she had in abundance. Not just Flurry the eternally beautifying. But the hive she had cradled once when she had been Crysalis. The hive she had wished to spawn in endless numbers. The dragons whose eggs would hatch into the mightiest of children. And the sea ponies, whos young were rocked by the gentle waves of the sea.
All these thought came together in an Chaotic harmony. And it made Cosmos feel all fuzzy inside. A tickling of an instinctual nerve that all living beings share. The instinct to create a continuous legacy and breed a new generation.
These thoughts reshaped the chaos energies inside her. And her eternally changing body began to swell. Fueled by all the love she was absorbing from all her endering children, her growing powers began to take new shape and purpose inside her.
Did she not wish to bring chaos into this world? Why not spawn it in the form of a brood that would be the mightiest of them all? Since her power would be forever growing, why not as well grow into a mother of all things? Since her form was to be forever changing, why not let her change into the goddess of life?
And most of all: This way. She would finally assert her dominance over that verminous poser Flutter-enquus. And infatuate deasest Discord, by solidifying all he power into a physical new essence.