Because the Sororitas also need their own tacticool edgy infiltration unit in a half skull mask.
Lore blurb:
A Widow is a stealth and assassination specialist of the Sisters of Battle.
Originating from the Cult of the Mourning, the Widows believe and acknowledges that the Emperor has been mortally wounded in his fight against Chaos. Though such belief would have been considered heretical in other places, exceptions has been made for members of the Sororitas, for it foster a hatred of the enemy that is fostered not only by zeal, but also by revenge, each member seeking retribution in His name.
Believing the Emperor to be mortally wounded, the Widows do not call upon miracles, for in their eyes, he has already given mankind enough with his ultimate sacrifice.
Driven by hatred rather than zeal, the Widows are called upon for mission requring subtlety and stealth, or otherwise considered dishonorable or inglorious by others of the mainstream sect, for they care not of glory or shows of faith, only of hurting the enemy as much as possible through any means nessecary
