I think it has to do with the mode of transmission. Hormones are only within the organism, transmitted by the bloodstream to the target organ.

Don't certain female insects emit pheromones into the atmosphere as attractants to the males? That's been exploited in some pest control devices.

And they've even been found in humans, with receptors in the nasal passages of the opposite sex. For a while they were incorporated into some perfumes, as I recall; maybe still. (No, they're not aphrodisiacs at all, but they do seem to render the recipient more calm, serene, friendly, receptive.)

Pheromones were a sexy topic not too many years ago; there ought to be a lot available via google.