I agree that you can do well with the dining plan - we have on past trips.
Sometimes, though, as I've stated every time this topic rears it's head, it's not about the money...
Sometimes, people want to just not mess with figuring out costs of everything every time. Sometimes, they don't want to mess with gift cards or credit cards or anything else. Sometimes they just want to order what they want and not worry about it. Do they sometimes lose money? Probably. But sometimes it's not about the money.
And just like politics and religion, no matter how loudly or how many times you preach your beliefs, you are just not going to convert people. And that's OK.
Can we all just agree to disagree on this once again, and move on?