There's some interesting discussion going on about antidepressants, which is somewhat similar to discussions about add medication for kids. 2 points: (1) Psychiatric diagnosis is often like the BMI, true at a population level but not necessarily true at a personal level. (2) Pathological is relative to the environment to need to live in. If school requires an 8 year old to pay attention in a class with forty 8 year olds for seven hours a day, inability to do so is often the trigger for medication.
With depression, I think it's uncontroversial the environments can play a large role. If the first course of treatment was living better, and medicinal treatment was layered on top of that as needed we would have better results with fewer side effects. OTOH, there are limits to what a doctor can do.
My earlier comment is more about 'why 40 year old men' not 'why depression.' The latter is almost certainly the more important and actionable question though.
My point is that many times we are not aware what is it that makes us feel bad and we just build a narrative that could or couldn’t have anything to do with our feelings. A good advice is, I think, when feeling bad; try to change how you spend your time and you can be surprised. Don’t trust too much in introspection.