That's kind of an odd perspective. Lots of things humans do don't "serve any purpose" other than entertainment. Get rid of movie theaters?
The cruise industry deserves a lot of criticism and should probably get some regulation. Coming at this from a perspective of "I don't find cruises interesting so let's get rid of them" them does not, to me, sound like a good strategy. Personally, I have been on one cruise and I really enjoyed it. The price was really good and I'd even do another cruise at a higher price if that was the impact. I enjoyed being on a very nice hotel that I could wake up in a new place each day.