For me, because I love to cook, and having a large kitchen just makes everything easier, from storage, to prep, to photography, to serving, to cleanup.
Right now I have a very small kitchen and it is a hassle to cook or prep almost anything, due to the lack of counter space. If you add another person into the mix, it is almost impossible to do anything.
Many times, I have multiple dishes being prepped, and cooked, and baked at the same time. I have to plan everything out in advance, and often end up using the kitchen table, and other areas that are not the kitchen, which I hate. We only have a single oven, so on holidays, the turkey (which my Mom makes) has to be done in an electric roasting pan in the laundry room, while pies and other things are being made in the single oven, in shifts.
Trying to prep a bunch of vegetables and fruits (for freezing, snacking, or other dishes that will be made later in the week) is a pain in a small kitchen, because there is nowhere to lay out everything at the same time, so it takes much longer. Baking is also a chore. Plating is a chore, cleanup is a chore.
I like efficiency, and a large, well set up kitchen is conducive to efficiency.