Why the skill dices, which come up with 1s, may be rerolled on push.
Because you want to become better at what you do.
The incentive angle never occurred to me, but I like it.
Conceptually, pushing dice means using extraordinary effort on a specific task. Base Dice represent raw ability, and pushing that risks straining or exhausting the ability used. Pushing gear, likewise, can break it. Skill Dice represent knowledge, experience, and practice, plus circumstantial modifiers; it's hard to imagine "breaking" any of that, so 1s have no special effect. Improvement typically has no downsides, so adding Skill Dice doesn't increase the chance of straining something.
Conceivably a pushed roll could simply eliminate Skill Dice that come up 1. (That would simplify probability calculations a bit.) Being able to re-roll 1s on Skill Dice gives the character with more Skill an edge over an opponent relying on higher attributes or gear, even if they're rolling the same number of dice.
It's also worth noting that only Forbidden Lands
and Mutant Year Zero
distinguish Base Dice, Skill Dice, and Gear Dice. In Coriolis
, Tales from the Loop
, and the upcoming Vaesen,
all dice in the pool are the same; 1s have no special significance and are re-rolled. (Alien
's Base Dice behave the same way; its Stress Dice do something else entirely on a 1.) One could regard Skill Dice as the "default" and Base and Gear Dice as special cases to represent wear and tear on bodies or equipment.