One of the obvious reasons that I can't think of is the lack of genuine personality in social media platforms. Everyone is showing off the part of them that isn't real or the side of their personality that is sugar-coated by their fantasy of themselves.
Although social networking isn't particularly a bad thing. It's the way we utilize social media that is making it detrimental to one's social behavior. Some of us would rather spend time behind the monitors / screens of our mobile phones when expressing their social interactions to one another. The act of personal approach to one another is getting lost along the process.
The social media of the present is becoming like an "AI" personality, it's redundant and consistently repetitive like an algorithm.