How do they get those "casual" folks back to their cabins? Transporters?
There's not much happening in the passageways on the cabin decks or in the elevators and stairways.
That's the problem they've created, by creating a casual dress public area for evening dining. They honestly don't expect those people to go to dinner and then directly back to their cabins... so their policy is uneforceable, and they don't bother trying.
Yes, it's a problem. Princess originally had entertainment on the Horizon Court on the Sun Princess class and in the disco/night club, located in the "spoiler" over the fantail, on the Grand Princess class, but it seemed to fall victim to the company's "cost cutting programme" a few years ago. I'm guessing that the new "Movies Under the Stars" program is intended to provide "alternative casual entertainment" at lower cost so that passengers who choose not to dress for "formal" evenings will have an alternative to stateroom television?