As with so many moral judgments imposed on women, it's rarely a case that some particular action or state is praised or blamed in abasolute terms, but rather that it is conditionally praiseworthy depending on how it upholds patriarchal ideals and structures. Being/remaining single may default to being discourged, but circumstances may elevate it in support of some other ideal or principle. Thus, the "widow faithful to her dead husband" is praiseworthy...unless she has failed in the higher principle of procreation.