Ranked Brawl Metagame Question.

How come all of the top decks in the ranked brawl event have been mono-color? As far as I can tell, this is how the meta seems to be forming:

Tier 1 Decks

Katara, Waterbending Master: Flash/Control

Phelia, Exuberant Shepherd: Aggro/Flicker

Rofellos, Llanowar Emissary: Stompy/Ramp

Tier 2 Decks

Yuriko, the Tiger's Shadow: Ninjutsu/Control

Lumra, Bellow of the Woods: Combo/Midrange

Etali, Primal Conqueror: Flip Etali

What makes all the mono-color decks so good right now? Nearly every deck I face is Phelia, Katara, or Rofellos.