This is one of the most interesting question to answer. I guess, it is due to invention of the Smart Phone and Facebook and the urge to be liked. One of the reason is social validation. Getting likes or those emojis make us feel good physiologically. There is this fear of missing out on the latest trends.
There is the self ego which social media platform gives us that feeling of self disclosure which lets user center the world around themselves which makes them feel really good as they can show off some of their interesting talents and skills or even things that they perceive others would go.
It also extends our offline world. This can let one to feel less lonely as there are many others out there.