Because it brings in a lot of people who are willing to pay for things naturally found in that country, like fudge, and lava rocks. They pay for food, hotels, and other specialties at slightly higher prices than the natives would pay, as they are on vacation, and have money to burn, mostly. They then leave, and more come in, it creates jobs, and as long as there are a reason for people to come, then they will. Also, i like ice cream.