Bloomburrow itself is a very two-color centric format, with some slight splashing, so doing more gifting of treasure would have been hard to pull off in such an environment
When we get competent tools to fight it, like Darksteel Citadel or Crucible of Worlds, they create a lot of value
They aren't in the rulebook, but they are the language of the players
Old Magic was full of cards with body horror and abstract nightmare creatures, but Niall Silvain somehow manages to be creepier than most of them
And last but certainly not least, Collector Boosters are the only packs that may contain a special Headliner card
It works as a silver bullet against certain strategies: Aggro decks hate it because creatures effectively lose haste, it slows down artifact decks that rely on churning out fast mana and rocks