A few guesses: social isolation, physical isolation (spending all your time in the same places, e.g. living alone and only leaving your house to go to work, or

A few guesses: social isolation, physical isolation (spending all your time in the same places, e.g. living alone and only leaving your house to go to work, or working at home), burnout, unemployment, unfulfilling jobs, childhood traumas (e.g. bullying, abuse), worries about the future (fear of ageism in their fields of work, fear of losing touch with technologies or current practices)... HN's getting more of those posts partly because you can create a throwaway account easily, and also because HNers have been warm and understanding of posters who may be depressed. In other communities there's a greater chance of trolls and griefers replying with personal attacks or suggesting suicide.