Why the love stories in The Last Tycoon don't work

Yes, the love story (stories) in F. Scott Fitzgerald's uncompleted novel, The Last Tycoon, are quite ridiculous and I'll be interested to see how the adapters managed to build a credible plot out of the shards that FSF left behind - and we have to believe he would have improved the plot had he lived to complete this novel. But really: famous producer (Monroe Stahr) sees 2 women who seem to be trespassing on the back lot during a storm and flash flood. One of them reminds him of his late wife; he manages to track her down (some confusion ensues as he first meets up w/ the other woman, not the one he's seeking). He encourages her to go for a ride w/ him; after seeming quite uninterested, she eventually goes back to his beach house and they have sex. Then he discovers a letter she'd left for him in which she says she's about to get married. Hm, I thought there was something here - maybe her husband-to-be in a fit of jealousy and rage attacks Stahr (or even his finacee, Kathleen Moore?), but no that doesn't seem to be what happens. After a long (chaste) 2nd date, in which she tells her sad and sordid life story - a childhood of abuse, followed by time as a mistress to a (married) man, a king no less!, somewhere in Europe, they part and the next day Stahr receives a telegram - she went ahead and married the guy. All OK I guess, but compare this w/ Gatsby, in which we really understand why it's so important to him to win back Daisy; in this novel, there's no real connection between Stahr and this woman other than her resemblance to his late wife. Another element is the crush the narrator - Cecilia (?), daughter of another producer - has on Stahr, and maybe she'll win his heart, but she's such an undeveloped character - FSF seems to forget for great swatches of time that she's the one narrating the tale - that we don't particularly care about her relationship to Stahr one way or another; in fact, we haven't seen them together except for a passing encounter on an airplane in flight. What does work throughout is FSF's account of the film industry in the 1930s - and of course that is what has drawn screenwriters to this tale at least twice. Anticipating the miniseries The Last Tycoon and thinking the more it can show us life in Hollywood (and the less that hangs on these tepid romances), the better.