Because the problem isn't that the woman doesn't have a husband, the problem is that society is shitty to kids who don't have a father. That's the problem the woman is solving.
The comment above is implying that the woman is "a lazy, dishonest bitch" for not going and finding a boyfriend or husband so that the girl won't be bullied at school, which is a pretty clueless thing to say. The idea that a family needs a father in order to have any worth or be treated with any respect is the cause of the problem in the first place, and this comment is just reinforcing that ignorant and incorrect position.
In other words, the reason the woman needs to hire someone in the first place to keep her daughter safe is because of people like the person who posted that comment.
Personally, it's the "Her mother is a lazy, dishonest bitch who bought a fake father rather than finding a real one for her daughter." part of the comment. It's very strong language that I don't think is deserved and it makes it sound like finding a new father would be easy.
There's a well documented reason why there are a lot of single men in Japan.
The reasons behind _that_ aren't so well understood but generally seem to be disillusionment with the idea of falling in love, getting married and having a family, unwillingness to fit in with traditional expectations (housewife taking care of the kids + hard working salaryman husband) or simply seeing relationships as too hard.
Western men are deeply conditioned to feel sorry for women in all circumstances. Even when that sorry-feeling is not warranted. They would have no problem understanding that a man doing the same thing to a child is a dickhead, but a women doing it, is a victim of bad circumstances.
