When you don't know how to deal with your emotions, you feel an urge to dump them onto other people to see if they know how to deal with them, or else it builds up inside you, getting more jumbled and hard to unravel. Just knowing you're sad because you didn't sleep well changes your whole view.
Yeah but I also see it as a social thing in the Fandom. Everyone overshares. It's how social interactions work. And if you don't have a stance you are called out for it. Popular people do it constantly shows it's not something unique to individuals, but how the Fandom communicates.
I think it might be a symptom of people who haven't had to develop a "professional" persona, separate from their personal. You have to draw a line between what you share with your inner circle of trusted friends and family, your burdens and opinions, and what you share with strangers.