I’m not sure if on-line “social” (if you can call it that) activity is more powerfully stimulating than IRL social activity. I kind of think the opposite, that it’s quite lame, except that one can make up for that by spending endless hours doing it.
That said, I also suspect that on-line “social” activity pings just enough of people’s “social needfulness receptors” that it sorta-kinda satisfies people’s social urges. Combine that with the relative physical ease of on-line “socializing”, vs the actual effort one must expend to physically get off one’s butt and get out there, along with the easy opportunity to spend endless hours at it – the result it, for a lot of people, that on-line “social” activity becomes the course of least resistance, and that’s what people end of doing.
But I agree with Martian Bigfoot’s analogy with drugs that bind to receptors and displace other more natural actions of those receptors, not always beneficially.