Lost in Le Havre?

Something that confuses a lot of people about cruising is destinations/ports of call. You think you’re booking a cruise to Rome and actually end up somewhere called Civitavecchia. You think you’re off to Amsterdam and end up in Ijmuiden. You think you’re going to Paris and end up in Le Havre.
So what’s going on? Are the cruise lines lying to you about your destinations?
Has the cruise had to swap destinations a the last minute?
Nope, none of the above.