Fuck the kitchen. It's a fucking restaurant! 
I know that but the fact remains that to cook a different option for each member of a pre-booked party takes time and if they have to wait for you to get there and order you will have to wait ... this leads to complaints from customers so they ask you to pre-order.
You could go to a restaurant that does faster food but you are unlikely to get anything other than pre-cooked food that they have had delivered ready made and they have microwaved back to life.
Somewhere like AWT's place will be able to accommodate you but you will not get Christmas lunch type food. Steaks etc are what can be prep'ed and cooked to order. A roast, which is what most Christmas Party diners are seeking, takes time.
Think about it for a minute. How long does it take to roast a turkey?
