There are 6 most frequently used and evergreen card types in Magic: artifact, creature, enchantment, instant, land, and sorcery
Changing the as-fan of rarities (that is, the count of each rarity of card you'd expect to see when you open a booster), introducing more variance in slots, adding in more "outside" cards, all impact how the set plays and thus requires us to change how we build the set
Also they were careful to include a defiant look on Lillianas face and a spell in her hand to show us shes not taking this lying down
Lore-wise it clues you into the mind of Yawgmoth, who's now recognized as a person to the possibly unknowing audience, but also makes the player feel as though theyre some sort of dark mastermind themselves
It has better support for its theme, better value overall, and better cards
Leyline Immersion and Heroes' Podium let you accelerate and double-down on your legendary synergies