No one is making up rules except for Disney. They are allowed to make the rules because it's their park. What is stupid is they make the rules for the
DDP so confusing and they keep changing them. That's not anyone's fault. That's why this is even a question and why there has been so many people all over these boards verifying that you are not supposed to share meals on the DDP. Just to keep things straight:
You can always share a meal if you pay OOP in any restaurant.
You are technically not allowed to share and / or split a meal if you are going to pay with the DDP. After further research, basically when using the DDP Disney considers a meal anyone seating in a seat at a table eating. When you are on the DDP, you use a meal credit to purchase your meal. You don't purchase an entree, you select your entree of choice for your meal. Disney portion sizes vary depending on the entree. If you order chicken you may get a much larger portion size than someone who ordered steak or lobster. Some people may not eat all the chicken and it goes to waste. Disney doesn't do 1/2 orders of an entree or only charge 1/2 price because you only eat 1/2 your food. A guest does not determine the portion size of a meal. Therefore, even if only 1 person at a table for 2 orders a meal but both people eat, the party is supposed to be charged for 2 meal credits because both people ate a meal. How much they actually ate makes no difference. You can't eat 2 meals then tell the restaurant you only want to pay for 1 meal.
Anecdotal evidence from someone claiming Disney allowed them to split a meal is not helpful. No server ever wants to be put in the position of being the meal police and ruin their chances of getting a good tip; plus, they don't make enough to deal with the aggravation either. It does help a server out if the other person in the party who doesn't want to use a meal credit at least orders an appetizer or something. That makes it easier for the server to look the other way or explain why 2 people were eating but they only charged for 1 meal credit if the server was questioned by a manager.
I know this is confusing; but, not my rule. It is unfortunately just another frustrating and unfair quirk of the DDP that all of the DDP fanatics won't admit to. We won't hear about them "disallowing" it because it always has been the rule and didn't change when they changed a rule allow people on the DDP to use their meal credits for people not on the DDP.