When I started cruising in my 30s I disliked 'dressing up', in part because my Dinner Suit trousers and black broque shoes were too tight!! But over the decades with properly fitting clothes I got to enjoy the 'special' nights, IMO when the vast majority dress up it is a nice sight and atmosphere. We have mostly cruised with Cunard since 2015 but even they seem to be reducing the amount of Formal nights (or whatever they call them now) to the point where for long haul flight, far flung, flight baggage restricted weight cruises it hardly seems worth packing the Formal clothes.
We go on a land and Princess cruise South America tour this winter (1 week land, 2 weeks cruise, 1 week land) so we won't be taking Formal clothes but I'll be making do with Chinos and Polo shirt type look which I can also use on land evening meals.