I think my brother in law and his boyfriend can exemplify the answer to this. They love to go to Old Chicago and drink Old Chicago Iced Teas, which is their version of the Long Island, but made with 3 flavors of Smirnov I believe (orange, vanilla and something else). It tastes like juice, they go down smooth and easy and get you fucked up after just one or two. It’s the kind of drink that sneaks up on you…you’ll be sitting there and then you’ll have 2 of them, you won’t feel any different, but you have to get up and take a leak, and you seem to have forgotten how to walk. But you have one and it’s so good you have another, and another and another. So, they end up drinking like 5 of them, and they have some food, after tax and tip, the bill comes to over $100, and in their mind, they “just had a few drinks”. Now, if beside the description and picture of this drink, it said $7 each, and underneath it, they showed Coke – $2.25, well, it doesn’t take a math genius to say to himself when he’s still sober, I’m going to have one (or two) of these, because I’ll be drunk after one (or two), and then I’ll order a Coke and that’ll save me $20, if we both do that, we can save $40, that’s almost half the bill, we could actually come here twice as often if we did that.
But in reality, they won’t come twice as often, they’ll go to OC whenever they want to drink OC Ice Teas and have pizza, they’re not going to crave that experience twice as often, now they might go OUT twice as often, but they’ll probably go somewhere else. So the restaurant makes 60% of what it would have made. And because basically restaurants generally LOSE money or at best break even on the entrees and make virtually ALL their profits on beverages and appetizers, having someone drink 2 of something instead of 5 or 6 of something is a big hit to the bottom line. And not everyone who sees the price on the menu will limit themselves to 2 (or will be able to stop themselves at 2, even if they decide to do so while still sober), but enough will that it would be downright stupid for them to advertise the price.
Also, consider this. You go to the store to buy a PS3, you know that it costs Sony more money to make that thing than you’re paying for it, even though it’s outrageously expensive. And you get a blu ray player to boot, so you feel OK, it’s worth the high price. But if you went to the gas station to buy milk and it was $3.99 a gallon and the grocery store across the street was selling it for $1.68 (exact prices in my neck of the woods), you might think, fuck the gas station, I’m walking across the street. So, alright, consider that if you buy a 750ml bottle of each of the 4 liquors that goes into an OC Iced Tea, it would cost you about $60. But you’d get 25 drinks. $2.40 to get the same thing that costs you $7 in the restaurant. You start to put those numbers out there, SOME people (not all) will do the math and say, fuck this, I’m drinking at home.