Because we relate to other vertebrates, especially mammals. We are extremely far removed from insects. Insects, in all their exoskeletony, multi-eyed and -legged glory are foreign and unrelatable. As an ecologist I see the value of insects and their place in the world, but I don't give two cents about the crickets or roaches I feed off. When 5 adult crickets manage to drown themselves in half a coke cap of water, despite all the other climbable bodies, you realize why they've never made it beyond their lowly place in the feeding chain!