I feel part of the problem is the expectation that humans are supposed to be happy. Happy is just a state of mind, not necessarily our default state. Depression and mental pain have their uses. They alert us, something is wrong - make a change! Working through pain, not self-medicating, strengthens you. Even if you 'don't know what's wrong', the unconscious WILL act out on, repressed childhood trauma, for instance.
We're destined to suffer, if for no other reason the horrific reality that we will all be annihilated one day. Everything beautiful in the world will be taken from us. Our existence will end. So happiness is not our default state, or even where we SHOULD get to. Why would it be?
There are certainly people who need intervention before they suicide, and people with real chemical imbalances (for people prescribed meds - -is this EVER proven scientifically? EEG? blood test?), but we conflate those people with others who are just very rightfully sad about the circumstances in their lives. Often these people (alcohol, food, drugs, phone) instead of making the difficult changes.