Cunard is probably the last and foremost bastion of formal cruise dress. I would not take a Cunard cruise without a tuxedo. You could get away with a dark suit but you will look out of place.
Now here is one thing. I live in Phoenix and because of the weather it is a very casual state. People have never worn suits to work gere as they do back east - it just doesn't make sense.
The same is true in Florida where it is always hot.
Cruises orginate from Florida nd most of the mainstream lines are based there. They tend to take on their local culture.
Cunard is still a British company even if its headquarters are in Miami - all of its management are british.
Yes, it is too bad for the people who like to dress up that you are not going to find many non-luxury cruise lines that insist on fornal dress, and some of the more lux lines were casual before the mainstream lines went that way (Windstar comes to mind).
Truth be told, I dress up because I represent CruiseMates when I cruise, but if I did not I would be more casual. I also skip formal nights regularly because I just don't feel like getting decked out.
I always thought the formal dress requirement was more of sa detriment to the success of cruising than a benefit. A cruise is a VACATION first and foremost - and so it should be expected that some people will dress down. You know some people wear a suit to work 50 weeks/year and they don't want to do that on vacation.
I also don't care for tattoos or mullets, but I can't stop other people from choosing to look the way they want. Times change and yeah, I guess I am just getting older.