Why Northanger Abbey was accepted for publication in 1803 and not published for another 15 years (Henry Austen finally bought the rights back and had it published elsewhere) has long been a source of mystery in the world of things Austen. The introduction to the edition I am reading (which combines The Italian and Northanger Abbey into one gloriously compact, 688-page Signet edition) suggests that the publisher, having invested in the success of a highly profitable work, The Italian, did not want to risk publishing a parody of it, to possibly offend the author or damage the brand, as we would say today.
Indeed, though the introduction does not suggest this, if you subscribe to this theory, it seems possible Crosby bought the manuscript expressly to prevent it from being published. Sinister indeed!
But it also true, as the introduction points out, that Northanger Abbey is less a parody of Gothic novels than a mockery of their too-credulous readers, personified by Catherine Morland. It is, indeed, a novel about novel-reading, and as such sometimes strikes an astonishingly metafictional note:
"I will not adopt that ungenerous and impolitic custom so common with novel-writers, of degrading by their contemptuous censure the very performances, to the number of which they are themselves adding -- joining with their greatest enemies in bestowing the harshest epithets on such works, and scarcely ever permitting them to be read by their own heroine, who, if she accidentally take up a novel, is sure to turn over its insipid pages with disgust. Alas! If the heroine of one novel be not patronized by the heroine of another, from whom can she expect protection and regard?"