The answer to this question can be found at the beginning of Chapter 26, when Huck, with the Duke and the King, have entered the household of the Wilks, as the Duke and the King have impersonated the dead Peter Wilks in order to gain his inheritance and property. They have been successful in their first meeting and that night the Wilks girls cook them all a dinner:
Mary Jane she set at the head of the table, with Susan alongside of her, and said how bad the biscuits was, and how mean the preserves was, and how ornery and tough the fried chickens was - and all that kind of rot, the way women always do for to force out compliments; and the people all knowed everything was tiptop, and said so - said "How do you get biscuits to brown so nice?" and "Where, for the land's sake, did you get these amaz'n pickles?" and all that kind of humbug talky-talk, just the way people always does at a supper, you know.
Twain can be said here to be making light fun of Southern hospitality, and the conventions that dictate that the cook must insult their own food only to allow others to have the opportunity of praising it and saying how wonderful it is.
To get complements from the guests. They know there food is good.