It seems plausible that social media is part-cause, part-symptom of a larger shift away from "real" socialisation. I don't have any scientific evidence for it, so feel free to debate. In general in doesn't seem like a controversial opinion to notice that how we are, socially, has changed over time, probably not for the better. It might be that it's hard to pin down one major cause, because the whole system is moving in tandem.