So if there isn't a cop enforcing the speed limit on the road today, it doesn't exist?
Now you're comparing apples and oranges...One is a law that is black and white the other is a document open to interpretation.
A better comparison would be if you were to get pulled over for speeding and you don't get a ticket. It doesn't mean you didn't break the law, or that the officer doesn't believe in the speed limit. It simply means he chose not to enforce it at that particular time.
However, let's take this a step further. Let's say people always drive 10 miles over the speed limit on this same road. The cops never pull anyone over ever. Until someone comes by doing 15 over the limit, and they get pulled over and they get cited a ticket. The speed limit was the same in both cases. It's just that at 10mph the officer didn't feel the need to issue a citation. 15mph was his limit he felt the need to take action. That's at his discretion whether we agree or not.
It's exactly the same at Disney. They may not enforce it with park attire. But if you come in dressed like Uncle Eddy from the Vacation movies with a tank top, cut offs, and a pair of flip flops and socks, they are probably going to say something. Does not mean that the people in park attire aren't "breaking the rules". It just means that they choose to ignore it until a certain level.
It's funny you mentioned "entitled" because from Disney's perspective they could see you as entitled yourself. To be clear, I'm not saying you are at all. However, if you were the only one complaining about people "under dressed" you would be outnumbered and Disney would likely try to accommodate you as best they could but would likely consider you the problem, not the under dressed.
Just like if every time you passed that officer and you stopped to tell him he should write a ticket for all of those other people speeding too....He'd send you on your way, and write the ticket he chooses to write and let the other slide as he decides.
I don't know Disney's reasons for being lax on a dress code. I don't work there so all I can do is speculate given the information in front of me. My speculation is not enough people coplain to make Disney waste their time turning a bunch of paying customers away for. Because at the end of the day for Disney, it all about that bottom line and mighty dollar.