So the parents decided to forget about the Reimu because they can't help her.
Interestingly, the parents never did forget about the wasa (excepting after the wasa is mangled).
Sure they had their bouts of stupidity, and what they were saying made little sense (stumped me a little until I realize those aren't supposed to make sense), but they did try to make the wasa suffer as little as possible.
And then they made babies and it all went to hell.