We've done Cunard dressy cruises and are finished with that sort of thing. However, on Viking cruises , ocean and river, we do change for dinner. I feel the staff has gone to a lot of trouble to present a nice dinner for us and that we should respect their efforts. We're not very dressed up, just showered and changed into a nicer outfit than the one we've worn all day.
People can, of course, wear what they'd like and we can draw our own conclusions about them.