It's weird how your experience trumps my experience and makes yours the law of the land and I'm "wrong".
I've served in our restaurants and I'm friends with a good portion of over 100 servers between our family's restaurants and my uncle's.
Not speaking to Disney, if you're in a place with a dress code that is met by the majority of diners and you're dressed however you want to be, you are judged negatively by the staff and guests.
Your service isn't going to be trashed or subpar, but the guests who dressed the part and met the dress code will be treated better and attended to more.
Still staying to the restaurant industry and not Disney World, I'm not sure if you're in a honky-dory fantasy land in your head, but the restaurant industry is notorious for negatively viewing African American guests and foreigners as poor tippers and foreigners with disgust and dread. Are you going to pretend that the food service industry doesn't approach minority tables with the assumption of a poor tip and being ran around? Because anyone even outside of the food industry knows that's a huge, recurring stereotype among food servers. But, judging people on their dress appearance is a stretch? Maybe in Applebee's, yeah. If you walk into a restaurant like Capital Grille or Del Frisco's not meeting the dress code, you're going to be viewed negatively and that you're 'out of place' and assumed that the tip is going to reflect it.
I'm not telling people to wear suits, I'm saying you should meet the established dress code that they have for a reason. But no, our self-entitled American society trumps that, where we acknowledge a dress code exists and literally say, "Nah, I want this food, but screw their dress code." It's weird that in Spain, Italy and throughout the UK, dress codes aren't an issue being met and I never see people in lounging home clothes at nice restaurants.
Anyway, back on topic. The dress code policy in Disney is not enforced because it was overran with guests not adhering. So, instead of dropping demand and sales by enforcing it, they've allowed it to fall to the wayside. A good 30% or more will be in park clothes at many of the signatures.