@FrogReaver, if the game doesn't list principles but instead relies on the GM to come up with those principles, there aren't really any principles at all.
@Aldarc has explained this in quite a bit of depth while I was writing out my own post, but I'll chime in nonetheless.
D&D has never explicitly called out principles the way PbtA games do. Snagging from the Dungeon World SRD, there are two main concepts that D&D lacks: Agenda and Principles. The Agenda is the GM's goal. In Dungeon World, the GM's "job" is to:
- Make the world fantastic
- Fill the characters' lives with adventure
- Play to find out what happens
The text explicitly says the following:
In D&D 5e, I'd say that the GM's principles are similar, save for the last bit. I believe "create enjoyable combat encounters" and "challenge the characters and the players" would replace the final bullet point, but your perspective may differ.
In Dungeon World, the GM's principles are thus:
- Draw maps, leave blanks
- Address the characters, not the players
- Embrace the fantastic
- Make a move that follows
- Never speak the name of your move
- Give every monster life
- Name every person
- Ask questions and use the answers
- Be a fan of the characters
- Think Dangerous
- Begin and end with the fiction
- Think offscreen, too
The purpose of principles is to establish how the GM runs the game. Actions that are aligned with those principles are greenlit; those contrary to them are not. These principles are all largely compatible with 5e, but I'd alter a few slightly ("ask questions and use the answers" is inappropriate), and I'd add "consult the dice when uncertain" and "balance risk and reward." At least, that's how I view the designers' intent.
The problem within 5e is that everything is wishy-washy in terms of the non-combat or spell mechanics. There's no procedure or rules of play to guide the GM's hand. Without an Agenda or Principles, the GM is left to determine his own. Flexibility is a strength and weakness of 5e because D&D is in many ways formless; the rules have a structure, but because the game isn't designed for one particular use, it takes on the shape of the vessel into which it is poured...sort of.
Dungeon World is designed for high-action fantasy adventure. It tells the GM how to accomplish this with its Agenda and Principles. D&D has always lacked these elements, and it has never provided cohesive guidelines on how to run the game to accomplish the purpose of the game. What is the point of 5e? The point of 3e was a streamlined version of AD&D 2e that implemented character customization and tactical options. The point of 4e was to balance 3e around the tactical combat elements. The point of 5e is to...well, I suspect it was to appeal to the fanbase that had originally left for Pathfinder while remaining accessible to a wide audience.
The rules don't tell the GM how to do any of that, though.