Sugar gliders are not legal to own in California because the Department of Fish and Wildlife claims they pose a threat to native fish and wildlife, agriculture, and public health and safety. Many states have restrictions on exotic pets, such as sugar gliders, because they pose a threat in some way.
California takes the stance that introducing a nonnative animal could be detrimental to the habitat and wildlife of existing animals. Owners often become frustrated and tired of pets and release those pets into the wild and, on occasion, pets escape their homes. When this happens, the nonnative pet competes for food, habitat, and very well could introduce diseases previously unknown to the wildlife in the area. The government considers this a dangerous risk, and as a result, most exotic animals are illegal in California.