in my opinion, rather than attraction, it's more like just their mating instincts
Yeah by attractive I mean that they see them as good host for their offsprings or that they find them good for sexual release.
I know their are creatures in the world rumored to do it for pleasure other than humans, and some will do it with anything they can find.
But it is interesting how this same logic happens with monsters in so many stories.
Of course this is fiction so the real reason is usually that the authors want to add rape so the monster look just more despicable and killing them is seen as more correct.
Well some also do it to add fanservice, only a few actually take interspecific mating or hybridization too seriously especially for mindless monsters primative/low intelligence creatures.