Actual reason: Skirm doesn't swim in options to put skill points in I see no reason to further discourage usage of traps which are probably one of the most unpopular trees in the game already on the ONE
class that actually might end up taking it - rogues have better things to unlock and traps fit a ranged character so much better anyway. Could contribute ever so slightly to spice up a rather bland (but filling) class.
Skirmisher really is the mashed potatoes of tome. One might even go as far to try out mystical cunning! I think the balance impact would be minuscule so it won't like break the class (which I personally think is decent but not super op).
Reason I just made up: 1.00 masteries are a pretty outdated concept in general - the idea behind it seemed to be that classes are worse in skill trees that they "borrowed"
from other classes - in this case rogue is supposed to be the master of traps and skirmisher is just okay enough at it.
More made up reasons: a clean line of 1.30 masteries is aesthetically more pleasing
And always remember: Pace yourselves and take a deep breath to recover your stamina *signs petition*