Why might the death of a loved one cause enlightenment in some people?

 It is a meditation on impermanence in action.

You didn't want this but it is real and you cannot run away from the death of a loved one and go on.

For some it is a life or death initiation in that if they don't self destruct mentally and emotionally then they also might self destruct physically too.

But, for some rare souls it forces them into enlightenment where they begin to help themselves and all other beings ever after.

So, it is a forced meditation on the impermanence of human life here on earth and sometimes moves people to become completely enlightened in the rare souls capable of this without going crazy or dying when a close loved one dies.

Did losing my father and mother enlighten me?

Yes. But, I wouldn't want to go through any of that ever again and in fact I'm not sure I could survive going through something like that at this age (almost 73) and survive it now. So, it was a blessing in some ways that they died in 1985 (my father) and 2008 (my mother) so I was young enough and resilient enough to survive their passing still.

It was also difficult to lose 2 of my best friends from childhood as well. I lost one best friend in 2006 and another in 2011. I still have one best friend alive that I started climbing mountains with in 1969.