That is why there are many cruise lines to choose from. If the urge to dress up is too important, then HAL and Cunard are there. I used to get into the dress-up thing but eventually realized my personal comfort was more important - within reason.
But - when someone is seated at a table with a napkin in their lap, why would it matter if they are in jeans or shorts - or in a $200 pair of slacks? It isn't as though people are looking under the table cloth to admire the other guest's wardrobe. Please, nobody take this personally since it is just a general observation...but I'd rather have fun table-mates in shorts and golf shirts than be stuck with some crashing bores in tuxedos and gowns.