Actually, they are actively prohibiting food and drinks from outside which, while being easy enough to get around, requires you to act sneaky and deceptive... making you feel like you're doing something that's somehow wrong... possibly even criminal. And that's not taking into account that taking in hot and cold foods, particularly the sort one tends to associate with movie-going (but more on this later) is a bit more difficult than bringing in a candy bar.

And they're not just counting on people suddenly saying "you know, I forgot to eat and can't wait two hours for unhealthy food" and unthinkingly throwing money at the concessions stand out of pure impulsiveness. No, this shit is orchestrated.

First, they attract film-goers with the sight and smell of colorful and enticing foods to convince those who would otherwise be perfectly happy not consuming anything. Then they're sure to bombard you with advertising drilling it into your head that these are necessary staples of the film-going experience.

Package deals at the ticket counter pretty much always include concessions (no "family deal" ticket package is complete without popcorn and soda!). The brightest and most colorful area inside a movie theater (and one you can't get to the movie without passing)? The concessions stand. The advertisements before a movie? Interspersed with soda and candy ads (primarily soda ads - after all, a product that's mostly water has a massive profit margin). The video preceding every movie reminding people to remain quiet and turn off cell phones? Also comes with a friendly reminder that yummy food and drinks can be purchased in the concession stand (and please throw your trash away in the garbage can). And virtually every depiction of moviegoers in the actual movie shows them with at least a thing of popcorn in their hands.

Make no mistake, movie theaters aren't just resting on their haunches in the blind hope that you'll fall for their scheme. They have designed their business, their theater architecture, their advertising, the imagery surrounding their business, and the entire moviegoing experience around using as many social engineering tricks as possible to push you into giving in to that scheme.

The core sentiment you seem to be espousing, that ultimately what you spend money on is your own choice and movie theaters can't be blamed for trying to make a profit, is true. However, while taken at face value the complaints about concession prices are seemingly whining about a product that people don't need to buy, these complaints are actually, in ways often not realized by those making them, coming from the theater's constant barrage of manipulations drumming up demand for a product while simultaneously doing everything in their power to foster as much of a monopoly on said product as they can manage.

People don't like being manipulated, and when they see the prices on movie concessions, people can often feel that they're being manipulated, even if they can't quite understand how. No one's having this internal conversation with themselves, or they might start to put things together:

"I can't believe I have to pay this much for popcorn!"

You don't have to buy popcorn, do you?

"Well... no..."

Did you want popcorn before coming here?

"Um... not really..."

Do you know why you want it now?

"Well... it's kinda' an impulse thing."

Funny how that impulse always seems to strike when you go out to a movie, huh?

"Well, it's popcorn. People eat popcorn at movies."

Why?

"Umm... Well, it's a cultural thing. It's what you do, you know?"

So you don't want it because you want it, you want it because you're supposed to want it. Is that right?

"That's stupid. I'm a free-thinking person capable of deciding what I do and don't want."

Okay, you want it. You can always get it afterwards cheaply, right?

"Well... yes..."

So will you buy some after?

"Well... no, probably not."

Why not?

"Because I want it now, for the movie."

Is it your favorite food?

"Oh, hell no."

Is it your favorite snack food, even?

"No, I suppose not..."

Do you want it for movies you watch at home?

"Sometimes."

Even when there are other things you know you like more?

"Yeah, but it's a movie thing. It completes the experience, you know. Eating popcorn while watching a DVD makes it more like you're in the theater. Get the movie-going experience, you know?"

So you prefer watching movies in a theater to watching them at home, then?

"Well.... not usually, no."

But you have the movie-going experience, don't you?

"Yeah... but you can't pause to go to the bathroom, and there are annoying people there who make noise and cause distraction, and the floor is sticky, and the food is overpriced..."

So you eat the popcorn that you don't like all that much to recreate the movie experience you don't like all that much?

"It's iconic!"

Where do you tend to see that sort of iconography?

"... in movies..."

At the movie theater?

"... sometimes..."

So movies in movie theaters are the reason you want to buy things in movie theaters? Doesn't that seem manipulative to you?

"Oh, that's silly. I can't be manipulated that easily."

But aren't you at this very moment demanding a product you don't like to preserve the experience you don't like, when mere minutes ago you didn't want it and in a few hours you won't want it anymore either?

"Even if that were the case, it's not like they're actually trying to manipulate me like that."

They aren't constantly bombarding you with images of popcorn from the moment you step in the door, playing on the screen before the movie, and ensuring that every second you can look around and see popcorn somewhere around you?

"Oh, that's not manipulation, it's just advertisement."

Just what do you think an advertisement *is?*

"But that can't actually make people do anything!"

If it couldn't, then why would they do it?

"......."

... Wow, that was a long bit of internal dialogue, isn't it? The sort of introspection a person just doesn't do, right? And because they don't, the whole topic of manipulation never even comes up. Instead it's just a simple "I have to buy this" and "The prices are too high!", which is easier to wrap your head around than "The theater is bombarding me with imagery to make me want to buy something, and taking advantage of the impulsive spending they're pushing me into by raping my wallet".