Why can't I choose Human affiliation for my deck?
Humans have the most cards printed by quite a large margin; almost 4x the next most printed types, and 10x or more for many others, which creates a incentive to choose them simply for maximum deckbuilding options. This incentive goes against the spirit of the format's deckbuilding and is thus banned.
Is this a Comander variant?
No. Leaders do not count as Commanders for any gameplay purposes, do not start or transition to the Command Zone, and there is no color identity, command tax, commander damage, etc.
Aren't there already too many formats for Magic? Couldn't this just be a Commander variant?
Coalition offers a new and interesting way to build decks and play Magic. Other formats are great too, but Coalition is more than a spinoff or variant.
Does this have to be played competitively?
Not at all! Make sure your playgroup is on the same page about power level expectations, and be aware that the format was designed with high-power competitive play in mind.
Why not allow other legendary cards?
The choice of legendary creature should really be something special, not just another card in the deck that you happen to have easy access to. For both flavor and power reasons, they are the only legendary card decks can run.
Why does affiliation count more than just a creature's type?
There are plenty of creatures that synergize with creatures outside of their own type. For example, Kaalia of the Vast would not offer any interesting deck possibilities just based on the card's creature types of Human Cleric. Affiliation, rather than strict "cards of a creature type", addresses this while still allowing for decks built around a single creature type.
Doesn't the victory point system exclude play styles?
Winning guarantees 21 victory points, so you can try to win with any method you want. However, if you solely rely on an alternate win condition without accruing victory points during the match, you're taking on a lot of risk: secure the win and you're fine, but you'll be much further behind if you lose. It'll take creativity, skill, and some luck to make these playstyles work often enough to win you the entire match.
Why can't I run Shapeshifters in decks of any creature type?
Shapeshifter is just a creature type, so Shapeshifter cards are subject to the same deckbuilding restrictions as any other cards with a creature type. However, you may be conflating Shapeshifter with their frequently associated ability, Changeling: Changeling is not a creature type, but rather a characteristic-defining ability that gives a card with it all creature types at all times. Because of this, Shapeshifter cards with Changeling can be run in any deck. Shapeshifter cards without it, though, will have to be in a Shapeshifter coalition type deck.
Why does the turn order have to depend on victory points?
Going first in any format is a significant advantage; penalizing players doing well allows for balance across the multiple games in a match.
Why four of lands and creatures but singletons for other spells?
Coalition puts an emphasis on victory points as the win condition and creature types; the unusual deck structure keeps creatures consistent but puts much higher pressure on other strategies. It's also born from the format's original concept of hybridizing 60 card formats and playstyles with the popular singleton multiplayer formats.