I am sorry awful things have happened to you in life, but fortunately, as your example shows, negative external stimuli are not a 1:1 correlation with depression. Unfortunately, positive circumstances are also not a 1:1 correlation with the lack of depression. While stress, trauma, tragedy, loss, adversity may all push some people into depression, there are plenty more who, for no discernible external cause, find themselves in irrational states of despair or other forms of depression, and it is no more solvable through self-motivated resilience than the hallucinations of a more tangible mental illness like schizophrenia could be solved through resilience. Perhaps a useful way of thinking about it if you don't quite understand depression ( though maybe not neurologically accurate ) is to also think of depression as a form of involuntary hallucination. Only instead of an auditory or visual hallucination, the brain is producing an emotional hallucination.

As for the downvotes, it's probably because the tone of your comment, perhaps unintentionally, comes off as skeptical & dismissive of the miserable reality that many people experience first hand.

Finally, & unrelated, it looks like you do some very fascinating work!