The whole story is about them not being dangerous unless triggered, silly. Its a plot device
From what I saw in the raws you might want to take that back a little
Rip
For the MC his father was his person of comfort and someone who gave his life meaning. He's someone he cared deeply about. It's not crazy to be unable to accept your parents' death. For some people losing loved ones is worse than death.
This is so wird why would you keep your zombie parents in the house when you know you will get stacked every second and I don't think every parents would do the same for you also you will die if you live with a zombie