Homosex makes so much sense in social animals. Animals already know how to have sex, so using it to communicate with the same sex repurposes a preexisting feature. If reproductive sex increases social bonds already, why not use sex for increasing other social bonds? In this case, hooking up with another mother bear allows the entire unit to have better chances of survival. Your direct genetic offspring have a better chance, thus the tendency to fuck with both sexes gets passed on, as does the tendency to care for children other than your own.

Gex might play an important role in social animals' survival, and also their ability to have empathy with all members of your species, even if not directly related.