I have a hunch that they picked one - appetizer or dessert - because of turning tables over. It's just a hunch, but you asked me why.
If they can turn tables over faster they are making more customers happy because there are more available ADR's for each restaurant on any given night.
I don't know if I'd complain that it was appetizer and not dessert, I might, but I wouldn't get all up in arms about it. I'd simply order my included appetizer and we'd pay OOP for a dessert or two to split among the table. (which wouldn't do them any good in turning tables over faster with our crew!

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