Who knows really. Lack of community is a big one. Be interested to see the data. Suicides were often hidden or lied about historically as it went against God and would bring shame to the family.

talking about your problems or writing it down can significantly improve one's mood and in the long term increase resilience.

Yes, especially after trauma. Something to do with how language works in the brain. Telling a story about the event helps us move through it. Have you read The Body Keeps The Score?

Thinking of kids raised in households where someone dies and no one talks about it and how they become stuck with the trauma from it. Or the world wars where it wasn't manly to talk about the horror they'd seen and they'd resort to violence, madness, suicide, and still no one talked about it.