Depression is a fickle thing. Many people suffer from it, and many other mental health problems, a lot of those people also go undiagnosed, either though not admitting it and seeking help, or by thinking they can overcome it themselves. They find ways to cope, or overcome the feelings of depression and fight their fight in the best way they know. This, in part, is the problem. Turn to alcohol, or illegal substances, or posting memes on social media and no one really cares. But when you use social media to write about it, to out-right tell people you are feeling depressed or suicidal then they complain. The comments like "just get over it" or "it's all in your head" or "you're attention seeking" do not help one bit and those comments may just be the tipping edge that sends someone tumbling down the rabbit hole towards a path that will lead them to self-harm, suicide or such.
Leaving subtle clues about your mental state, and people are there to help, they say they will be there for you, and want to help you, but when you actually get to the point that you need that help, everyone disappears. It's a never-ending fight against mental health, trying to keep yourself in check, fighting back from that tipping-point, while some people, who try to offer "help" are actually the ones pushing you over the edge. Of course that edge will be different to everyone, and words that may help one person could be detrimental to someone else. The key is to try and find what will help the person involved. Not to think your coping mechanisms will work on someone else. If posting pictures of dogs helps you cope with your problems, it does not mean that it will cheer up everyone, although who wouldn't be happy to see a cute puppy!
For years depression has been painted in the media with a certain image and that stereotype has made everyone think depression is the same no matter who has it. this is the furthest from the truth as you can get. Depression has so many different faces, its that smile on a girls face as she laughs with her friends, its that jump in his step as he walks down the street, its the happy songs blasting out the hi-fi at a party. But its also not washing or combing your hair for weeks, being unable to move, those curt one word replies to messages. Until people understand that, they cannot help you. They need to know what works best for you, not what works for their depression.