I can't speak for everyone, but the contract fanfics I see thriving usually ditch the predictable 'and they fell in love anyway' ending. The twist that hooked me in one story was when the fake spouse, who was initially just a gold-digging side character, turned out to have been hired by the real love interest's family to test their loyalty. The fake spouse developed real feelings, sure, but the betrayal angle was a gut-punch I didn't see coming. It wasn't about love conquering a lie; it was about navigating the wreckage after the lie was exposed from day one.
Another popular route flips the power imbalance completely. Instead of the wealthy CEO holding all the cards, the 'poor' partner is secretly the one with the leverage—maybe they own the debt, or they're an undercover investigator. The reader gets to watch the smug, powerful character slowly realize they're not the puppet master. That delayed realization, the moment the contract shifts from a tool of control to a trap they set for themselves, is catnip for an audience tired of one-sided dynamics.