That's just ignorance. There are a wide range of cruise lines, each offering different atmospheres, itineraries, and amenities. Some cruise lines cater to a mass market audience. Those are less expensive, tend to frequent Caribbean ports, have adequate but lower quality food, younger and less affluent passengers, and can provide a relatively noisy, crowded environment. Perhaps those are the kinds of experiences your relatives are familiar with.
Mid-market lines like Princess and Holland America offer a different experience and are popular with a different kind of passenger.
There are specialty lines like Disney, and expedition lines like Llindblad, for people seeking specific kinds of experiences.
Upscale lines like Regent, Hapag-Lloyd, SilverSea, SeaDream Yacht Club, Seabourn, and the like provide a completely different experience at much higher price points. The ships are smaller and less crowded, the cuisine is outstanding, service strives to be world-class, destinations are global and more interesting, the ratio of staff to passengers is higher, and their passengers are affluent, well-travelled, and older.
You can read reviews here:
https://cruisetruth.com/latest-ratings-of-worlds-top-ten-cruise-lines/
Get an additional sense of each line here:
https://boards.cruisecritic.com/