The endangered species list is based on facts and population studies, its not some willy nilly save the furry little bunnies. Although I do feel bad because when it comes down to it, your average majority of people would rather save an animal thats cute and cuddly thats on the list rather than your "viscous" looking insect or reptile.
I suppose you could say it is all the "beautiful" or "cool" species. They make the best trophies / pets and they have the best skins, teeth, furs. Of course this isn't always the case.