For me (just related my own suicidal thoughts in my podcast), I think it comes down to certain combinations of triggers.
1. Immense pressure to be more
2. Pressure to conform leads to lack of authenticity
3. Constant talk about mortality
4. The FOG that dominates the culture and breeds severe depression
5. The lack of care for this life because it doesn't matter apart from earning a better one through drudgery
6. The constant talk about this wicked world and how awful daily life in it is robs people of the ability to see any beauty around them, another contributor to severe depression.