Huh. I don't think I ever noticed the tentacles climax before (to be fair, I only recently noticed the ones that pop out the floor can grapple you if you're naked). And I think facehuggers, by Aliens lore, only lay eggs when the victim is unconscious (no resistance), so maybe that's why. I mean, think about it, they fuck her throat, toy with her to make her orgasm, her heart rate skyrockets, she uses more oxygen then passes out. Then bipity bopity, her chest goes popity.
That's just my theory anyway. As I've started a bit before on this thread, I only came here for smut so paying attention to details isn't my strong point with this game.