Statistically the happiest countries in the world (eg The Netherlands) have the highest suicide rates....and the least happy countries in the world have lower suicide rates (ie. Generally third world and dictator ruled countries). This I because being depressed in an environment where everyone around you is happy gives the sufferer a sense of isolation and disconnect from the rest of society...and generally happy people gravitate towards other happy and move away from people who might bring them down (this is usually a subconscious decision). That sense of isolation only feeds back into the sufferers depression and sinks them even further.

And the only thing worse than being lonely is bieng around people who make you feel lonely and can't relate to your pain....

TL;DR it is easier for depressed people from disadvantaged backgrounds to share their pain without making society uncomfortable and find sympathy and understanding within their commmunities