I think "people" is skyrocketing it a tab-bit too generally, and that "less interactive" would be more accurate. Technology is not the sole culprit; though, that said, such does not take away from the point in which mass production, adopted social constructs (adopted by your children and their children, and theirs, and so forth), governmental and societal dependency on the online world (Internet, social media, games, etc.), and other elements begin to facilitate a kind of...culture. Perhaps, even lifestyle or entire means of existence is not going far enough. In any case, you no longer want the online world - you *need* it - and you're nothing without it, now increasingly true even for the simplest of nations. It is this dependency - no - tendency which breathes life into the one thing we all consume, the same thing that, supposedly intended to draw us together, has rent society part. As for the feeling lonely and whatnot, for people who - already - do not interact with others as much as they psychologically (and often physically) should, health disorders are surely to incur. You know things have come a long way when your own grandmother prefers to text you "Happy Birthday" than call and hear your voice, or a student with his entire life ahead of him prefers company from hundreds of unknowns on Chatango whom he considers better "friends" than real, breathing people. One's brain physically, or neurotically, changes to adapt to the way in which its user most operates, reconstituting habits, tendencies and other important facets of personality as one in turn reconditions their lifestyle to cater to a more virtual, instantaneous, and ideal world - the world in the machines. It is at the point where some people quite *literally* do not know how to appropriately and effectively to interact with an entity they're not communicating with as several billion bytes, or acknowledge something that isn't displayed as thousands of pixels before gaining our interest. So, I guess the answer to your query is not all that impressive or extraordinary: lonely people feel lonely because they are quite simply...alone...at least, that's my view.
EDIT: Almost exactly what Mokrie iterated. Give the man a win/like.