First of all, you don't have to come close to 15 drinks to make it worthwhile. Just over half of the cost of the 60 goes towards gratuities and wifi. Then you have the peripheral stuff such as ocean now activation, medallion shipping and the two casual meals. Basically you just need to spend just over 20 bucks in drinks to make it worthwhile. And that doesn't have to be alcohol. Bottled water, specialty coffee, canned soda, and fresh squeezed OJ can all easily make the number, so even if you don't drink alcohol, it can be worthwhile.
But, many teetotalers just automatically assume that it's not for them. If you only drink tap water, regular coffee, lemonade and iced tea, then don't get the package. But there are many cruisers in the 25% that don't get the package don't realize that in fact you can make it worthwhile without consuming a drop of alcohol.