I don't know why they are encouraging friends to apply for the Israel campaign, but knowing them, one reason is being able to track how many people go over there. Remember their fetish for number reporting? Secondly, there may be a cultural orientation of some kind for the ones who register. G-d knows there should be. But of course there is nothing preventing a JW from just going over there on their own, as I have known some to do.
Think of this as registering for a tourism trip as opposed to making your own arrangements. There are pros and cons. The Society never said you can't go on your own. Your analogy to the IC is also weak because if everyone who felt like going to Hawaii went there for the IC, they could be overcrowded. There are better places to direct your general anger than at attempts by the Society to organize its events.