The DDP is pure marketing genius on Disney's part. As thunderbird pointed out, the "bargain" DDP and the "convenient" ME keep guests at the parks, spending $$$. And Disney KNOWS that appetizer, entree, dessert, and beverage for every single adult at a table is too much food; couples or families not on the plan often share appetizers and/or desserts or just don't order them, so I think they are counting on people ordering
less than the total amount of food they were entitled to, particularly at those extravagant TS restaurants. And how many folks have mentioned their leftover credits t the end of their trip?
Disney sells you a Dining Plan that everyone staying in your hotel room
must sign up for, at a bargain price of just less than $40 a day per adult and $11 a day per child. Except everyone over 10 is considered an "adult" -- and I can't imagine many tweens ordering and eating appetizer, entree, dessert, and beverage, but they pay the full adult daily price, regardless. And lots of little ones under 10 (especially under 6) normally wouldn't even order their own meals anyway -- they'd share with mom and dad, particularly if there is a lot of food.
If you go to the most upscale 1 TS credit restaurants everyday, and order the most expensive appetizer, entree, and dessert on the menu, the dining plan is a real bargain. But not everyone wants to do that -- or can get the ADR's! And if you spend those credits at a 2 TS credit restaurant or show, or even at a buffet, each TS credit isn't worth as much, and you don't get as much bang for your buck.
There is an excellent calculator/spreadsheet on Intercot to figure out if the DDP would be a good deal for your family, based on where you will eat, how many total A and C credits you spend there, and how much your family typically eats. I found out that it will save DH and I a
little bit -- on vacation we usually spend $40-$65 per person per day for meals and snacks. We could definitely spend less, if we wanted to only eat only counter service, or bought groceries to eat breakfast in our rooms and snacks to the parks -- and we've certainly done it before when our budget was tight. But we want to enjoy our vacation, try fun new restaurants, something different than we'd get at home, have at least one nice sit down meal a day, and another smaller meal to keep us going with all that walking

So the DDP should work very well for our eating habits and we can relax and have fun and not stress about our dining budget.