An aunt of mine had two (or three?) miscarriages before having her first child. Each time she was absolutely devastated. Honestly I'm pretty surprised that anyone would find that hard to understand. I'm not really big on children (and am childless myself) but trying hard to intentionally get pregnant* , anticipating a child for months, preparing yourself emotionally, and even making space in your home for a child, only to have a miscarriage has got to be one of the most traumatic things I can imagine. Short of losing an already born child or a spouse. In the case of my aunt she went through a really rough time where she blamed herself and later God for her suffering. I don't think that's cultural at all. I think that's just part of being human.
As someone who isn't really interested in having kids it's easy to forget that some people really want them. It is baked into our DNA and has been since before we as a species walked the Earth. If the pregnancy wasn't an accident then it's no wonder people mourn over a miscarriage. As far as they were concerned it was their future child. And I say that as someone who is very much not pro-life.
* Conception is not as easy as abstinence-only education would have you believe. Some perfectly fertile couples try for years before successfully conceiving.