Why do we see depression in the world? Well, there can be several causal factors including genetics, traumatic life experiences, abuse in childhood (both physical and emotional), separation of a loved one, addiction to drugs (as has been shown in research on depression and addiction), and so on...
Can depression be increased by negative media? I think yes. If you constantly see negativity, it does affect your mood. That is why it is said to stay away from toxic, negative people.
It's a broad topic, anyway...I just shared my views briefly.