This trend probably started around a few years ago. Social media used to be just a place to show yourself off (and it still very much is), and then people decided to be creative and show the non-awesome parts of their life.

 

I’ll go through what I think are the reasons.

Firstly, and perhaps most shamefully, people are looking for likes. It’s just something meant to get people’s attention, and we no longer see distress for what it is. It’s more like entertainment to people who have been raised with instant access to information that doesn’t concern us; we’ve been desensitized to violence and extreme emotions and all it becomes is a little notification on our phones. Wanting attention is one of the (worst) reasons people put their bleakest moments on a pedestal for the world to see.
Adding on to the previous point, some may be fishing for sympathy. They want attention and people to tell them that they’re sorry. People can be lonely, and need sympathy and a person to vent to, without knowing who that person could be. (To be clear, it’s not always a bad thing to want validation, but I personally would never be among those who post pictures of themselves in distress to evoke an emotional reaction.)
Due to less and less social interaction, many no longer know how to talk to people about something that is upsetting. Posting about emotions is a way to express your emotions to people, without asking any individual person to help. This avoids placing any unnecessary burden on those who are uncomfortable with discussing emotions.
I’ve done a similar thing, not posting my face or any images, but rather, I wrote some words about my grandmother passing away on my ‘close friends’ story on Instagram. I wasn’t sure who to talk to, and so, I decided to write my feelings and I got a few responses from people who were comfortable with offering their condolences.
Some post these pictures as art. The person posting may see artistic beauty in a person’s crying face.