Theres just something about leading a unified army of Elves, Dragons, or Vampires into battle
Their expected match winrates are 65%, 65%, 70% respectively, which tells the story of the importance of post-board I suspect many brewers think of a maindeck idea and then come up with a sideboard if the maindeck idea is good
New world order In one of his articles, Mark Rosewater introduced us to the New World Order in their design process: They would make sure that the common cards as they are the cards that new players will have the most contact with will never be overly complex: They should be easy to understand and easy to play with, so as these players become more interested and start buying more packs, they will gradually start having contact with rarer, and more complex cards, making the learning curve less steep
Midrange decks have lots of removal, interaction, and strong creatures