When turning a card face-up for its disguise cost, its classed as a special action
Artificial scarcity also plays a part
everything you need to play Magics most popular multiplayer format
And it contains a solid collection of offensive, defensive, and utility creatures for almost any situation
You can certainly play Commanders with Polymorph/Scramble elements that aren't dedicated to the strategy, such as with Neera, Wild Mage or other similar 'hit a big thing' decks, but the power behind playing a dedicated, limited choice for what you intend to hit off of a flip can greatly boost a deck's capabilities, and win games out of nowhere
It's one of the most powerful cards around, so it shows off the awesome potential of a well-designed deck