In real life dating, as in pop culture, fatness is often treated as something a person has to overcome in order to be considered an acceptable romantic partner. The trope of the fat girl with the "great personality" ("great personality" being a common code phrase for "ugly" or "fat") who triumphs over dating adversity and finds a date who is able to see past the fat is commonly used in movies, television, and pretty much any other form of entertainment. An extreme example of this trope playing out is portrayed in Shallow Hal (which I hate to even bring up), with Jack Black's character literally being put under a sort of spell in order to be able to see the inner beauty of Rosemary, played by Gwyneth Paltrow in a freaking fat suit. In the end, of course, the spell wears off and he's shocked that Rosemary is fat—but eventually her great personality enables him to love her despite her size.
Rarely if at all are narratives used in which fat women's bodies are viewed as sexy in and of themselves, where said bodies attract mates because they are desirable. As we've discussed before, fat women's bodies are often desexualized, and fat sexuality itself is something that's seen as disgusting and undesirable. A movie with a fat heroine who is actively desired and pursued by men and enjoys engaging in sexual activities is the stuff "controversial" indie movies are made of. It's so counter to our common thinking that fat is a repellent that any narrative daring to claim otherwise is considered "fringe" in many people's minds. With the majority of U.S. women being lumped into the nebulous category of "overweight," you'd think the demand would be high for portrayals of fat women who aren't desired only for their personality. But so many women are used to it being drilled into our heads that our bodies are never attractive because of their size, shape, dimensions, etc., that we don't even think we deserve to see a woman like us experiencing the pleasure of being desired physically.
Of course it's important to develop a decent personality for any size woman, but fat women are charged with being twice as nice as the thinner girls. We aren't supposed to be able to lean back and not be overeager when someone shows a spark of interest in us, whereas thinness often gives you a pass on being worried about having to overcompensate for your size. Fat women are expected to focus all our efforts in the dating world on doing everything possible to make it easier for someone to look past our fatness. Dress monochromatically; don't eat in front of him; cut your hair so your face looks less fat; downplay your interests and focus on your partner's. Society, and in turn pop culture, reinforces these ideas and desired behaviors by only producing media that show fat girls who bend over backwards to overcome their "flaws" getting rewarded with love and desire, whereas more "sassy" fat girls only get to be sidekicks to some thin woman.
Fortunately, in real life we get to make the decisions about who is worthy of our time and affection. If we can empower more fat girls to see their bodies as sexually attractive and deserving of a partner who agrees with them, eventually the demand for pop culture that reflects our reality will increase. But first, we have to stop consuming the media that make us feel unattractive and undesirable in the first place.