Guillermo Del Toro's "At The Mountains Of Madness" got rejected because there's no love interest.
Sex scenes rarely if ever add to a movie plot unless that IS the plot
Sarah Conner banged a time traveller in Terminator and it actually applied to the plot by creating a paradox. It's one of the very few times that I wasn't sitting their thinking "WHY THE FUCK IS THIS HAPPENING?? WTF DOES THIS HAVE TO DO WITH ANYTHING??"
Apologies that it's a link to a paywalled site. I believe they allow viewing one video for free? (I can also give out up to 3 people one week for free, so if anyone's genuinely interested DM me—preferably not from a lemmy.world account though because federation problems mean I may not receive it for over a week.)
But I found this video and its part 2 very enlightening in terms of ways sex scenes can be used in a way that genuinely does enhance the story.