They've seen the kind of crap we put on tv. They've heard about the fan fiction books that are essentially trashy "romance" novels with the same names as Austen's characters. They know about it, and they're catering to it. This from the Guardian:

There's nothing like a happy ending, and when the latest film incarnation of Pride and Prejudice hits US screens it will be even happier - by an extra eight minutes. After screen testing, the Jane Austen adaptation has had an extra dose of schmaltz added by the film's producers to suit transatlantic tastes.

In Britain, cinemagoers were treated to the sight of Fitzwilliam Darcy, played by Matthew MacFadyen, and Elizabeth Bennet, played by Keira Knightley, enjoying a chaste kiss. The film ends with Elizabeth's father, played by Donald Sutherland, giving his consent when Darcy asks for Elizabeth's hand in marriage.

But from next week, audiences in the US can look forward to a passionate, moonlit, and very un-Austen embrace between the two characters, with Darcy sighing his wife's name over and over again as they stand in their nightwear on their bedroom balcony.

Executives at the production company changed their mind about the final scene and left the clinch on the cutting room floor. But it was kept in for US audiences, who, a marketing executive suggested, preferred emotion to be laid on thickly.

The decision has infuriated purists and film fans alike, with a petition being launched to have the extra scene included in future DVD releases and Austen fans in the US fulminating over the "banality" of the scene.