Never rely thought about it but from an evolutionary point of view it makes sense why. Rains would have very likely associated itself with the replenishment of water sources, leading to more available food and an overall improvement in the prospects for survival for the species. As a result, they would be more likely to pass on genes that would enhance their ability to detect rain through smell.

Makes you wonder if a carnivore species needed blood for survival. Would they romanticize the smell of a fresh kill like we do rain hmmm