There is no reason for it, these people just desire creepy inter-species stuff.
Um, excuse me? Many series have done fictional couples, and those that like them, generally like them for what they are (or could be, like in this case). Don't assume that everyone who likes this couple (and/or other interspecies couples) "just desire creepy inter-species stuff." You may not have to like it yourself, but that's a rude and stereotypical assumption to make about those that do. -_-
I see people saying this is cute. Perhaps that is why I don't find it cute?