Yup. It's annoying. I asked myself the same question: If my guests are all paying for all-inclusive food & drink, why does it cost so much more for the wedding dinner. I do get it to an extent. It's outside of the regular service they are providing both at your event and behind the scenes in the kitchen. They have to staff for it. But they are still making lots of $$$ off us!
Our package is $3300 for 25 people (and includes a lot of extras - flowers, photography, videography, makeup/hair, massage for 2, private dinner for 2 on the beach, soloist, etc.). Then it's $94 per additional person for dinner. This includes set-up, champagne toast, wedding cake, cocktail hour, etc. But these are also priced separately so, for example, I don't plan to add any extra wedding cake. We get a cake for 25 plus dessert, so that will save me $7 per extra person. Oh, BTW, this doesn't include the $5 per extra chair for the wedding ceremony! And, if we want our reception to go past 9, we have to pay $15/person per hour for EVERYONE. Don't get me started on sound systems, etc.
I'm sad to say that DWs are a nickle & dime experience.