Because if you are a place that specializes in other people's occasions, having someone who can write "Happy Anniversary" legibly and correctly spelled on a plate is a good thing.
Because maybe someday you will want to make a galette, or put something on puff pastry, and you won't have to buy the dough.
Because a pastry chef can contribute to the savory side of things more than most savory cooks can contribute to pastry.
Because it isn't hard to figure out if your desserts are bought frozen and then served up, even if you garnish the plate.
Because it would be nice to have something on your dessert menu besides creme brulee, molten chocolate cake, key lime pie and cheesecake. Oh and a scoop of ice cream, ask your server for "today's" flavors.
Because that VIP will really like having a custom dessert whipped up just for them.
Because even though its the labor costs that make having a pastry chef expensive, a good pastry chef is going to work to make the expense worth the money.
Because long after your appetite for savory fails, your appetite for sweet carries on.