It turns out that Grodd kidnapped Caitlin because he sees her as his BFF and someone who was always nice to him. Shes also somebody who can help him out with his new mission statement. Its a lonely life when youre a psionic-powered super genius gorilla, and thus Grodd is feeling lonely. So much so, he wants Caitlin to help him essentially recreate the effects of the particle accelerator explosion in order to create more creatures in the same mould as himself. By the time Gorilla Warfare came to a close, it looks like poor, lonely Grodd may have finally got his wish.