How do you know you got it on the ship? Did you take a plane/stay in a hotel/eat at a dining establishment prior to getting on the ship?
Unfortunately due to incubation periods, it's virtually impossible to determine for sure that whomever was the first to "catch" the virus actually caught it while on the ship and not in the 20 other possible places they may have been at before leaving on the trip. This is a bummer for you, but travel companies have been extremely flexible for nearly two years now, at some point they need to start drawing a line.