For some like the planeswalkers it is for technical reasons, while both can offer a great influx of cards immediately they are dependant on the board state
Here is how the archetypes looked coming out of development: Theros: Red-White "Go wide" Bant: Green-White Renown mechanic with pump spells Vryn: White-Blue Control with flyers (and spell mastery) Ravnica: Green-Blue Tempo Dominaria: White-Black Auras Innistrad: Blue-Black Graveyard Kaladesh: Blue-Red Tempo aggro/Artifacts Regatha: Black-Red Sacrifice Zendikar: Red-Green Midrange beatdown/creature ramp Lorwyn: Black-Green Midrange attrition/Elves Once the archetypes were chosen it was still early in the process
Voltron Samuts flash, double strike, vigilance, and haste make her a fantastic candidate for Voltron-style creature buffs
Remove the abilities from an X/X to destroy it, or even use it on a planeswalker that's temporarily a creature to add loyalty abilities to anything while leaving the opponent with only a husk
If I recall there are four, the Piracy first, Reconnaissance Mission with cycling, the Bident above that can be tapped with two mana on an opposing turn to force them to attack and then the recently printed Vehicle called The Indomitable
Shelter (4.065) Color protection
