With respect though Mike, "just wanting to eat & go to bed" isn't having dinner, it's just having something to eat. My argument with cruiselines is as I said, why have these codes if nobody upholds them & if most don't want them it's a waste of time. I would say on the lines I use most, P&O & Cunard, a good 95% of people observe the dress codes & almost all men wear a DJ/Tux. People look forward to these nights too & like the chance to dress up.
I personally don't care if they have codes or not but just wish they would stick to them if they do. Like on one cruise I didn't pack a jacket for semi formal (jacket required), night. I stayed in the cabin as I was told I could only use the buffet & outside bars (no big deal I wasn't that well) but my wife said there were many people without jackets even the MDR, but as I had asked I did what they said.