I think it’s a sign of the Bennets’ gentility. I mean, I don’t think the girls actually do any cooking at all (can you imagine Lydia burning water?) , and Mrs B is genuinely outraged at the slur on the class of her daughters. It had become something of a badge of gentility to be able to support one’s womenfolk in idleness (apart from the eternal home dressmaking and mending, as well as the kind of embroidery that could be done in front of visitors (rather than darning your smalls), but it’s not entirely clear to me whether JA intends this as a sign of faulty parenting. It’s true that once Mr B dies, if no daughter has married well, five girls and their mother will be living in small rented rooms in Meryton with one maid of all work…
Charlotte, who clearly has more domestic know-how, will clearly be far more capable of running a small household, poultry etc than Lizzy would have been if she’d snapped up Mr Collins — but in RL, JA and her mother and sister did cooking, preserving, cheesemaking etc with their servants, though JA got a pass later in life when she was an established writer.
I love how JA uses food to make social points, like the difference between the Longbourn (rural, unfashionably early) and Netherfield ( Londonish, fashionably late) breakfast times. Lizzy gets Jane’s note about being ill at breakfast and has time to put on outdoor clothes and walk three miles cross country before being shown in to Netherfield, where they’re only now having their breakfast.