While your point is well- taken, the amount of promotional consideration Disney receives from exclusively promoting Coke products is likely tremendous - their contract is so tight, you literally cannot buy a Pepsi product on Disney property, even at the third-party owned gas stations. It has been established in the past that it is a myth that Disney gets it for "free", but they also do get a very severe discount/subsidy arrangement which is why Coke is so prominently branded all over those cups and stations, etc.
That said, even if it costs 50 cents (I'd guesstimate it is more in the 30-cent range, but have nothing other than assumption on that one, like anyone else), that really is "pennies" to most people (conceptually if not technically) when you compare the cost.
I'm from the North East, which is one of the most expensive places in the nation for food. So I used to think the prices at WDW were decently reasonable. That has markedly changed in the past ten years or so, and really so much so in the last few. I mean, $13 for a fast food burger "hot" off the warmer with a small handful of okay-if-you-douse-in-ketchup fries? With this price increase on drinks, with tax we are hitting $20 for a fast food meal. So a family of four is looking at $80 for what is really a small amount of food.
Some will compare this to a movie or a football game, but clearly - this is different. Those are individual vendors trying to make ancillary money - either the theaters, or those running the sport venues. In this case, it all goes to Disney. The problem is, Disney finance treats each restaurant like it is independent, which is one reason we have seen such extreme cuts in quantity/quality and such massive increases in price. You also don't spend a week eating at those venues - most people don't even eat a "meal" there if they are smart ("fork and dine" excluded), let alone three meals a day for a week when captive on property.
That's where I think this bubble will burst ultimately with Disney - it's no longer just a premium hotel cost to stay on property, it is starting to cost so much more to stay on property to eat that you can easily cover the cost of a rental car just eating a few off-property meals. And people who have cars can go other places, too - like Universal. It is taking us back before MYW, when they almost made it seem a bargain to stay for longer. Everything else has gotten so expensive around it, the savings on admission looks worse and worse every year.