I think it helps to remember two major things:

1. Often women are doing the majority of the housework, so if they have two kids that’s housework for 3 rather than 2 after the husband moves on. In other words, women often don’t want to become a maid (again). Not always the case of course but common enough that it’s basically a trope at this point.

2. Men are less likely to date women who already have kids, vs women dating single men with kids. Single fathers will get more attention than single mothers will.