> And why do people think someone just going offline will magically start talking to people (where? with whom?)
Necessary (but not sufficient) for change in life to occur is for the person wanting change to desire it happen and make effort for it to happen.
To answer where: whatever activity you choose to do with other people, assuming you choose an activity that can be social - typically something based on your interests, and if you're not sure what those are, try a bunch and see which ones you enjoy. Part of building a social circle is developing interests of your own and then finding people who share those interests with you.
To answer with whom: the people that are doing these activities that are there to do them but also be social. There are tons of places out for hobbies and activities where you can meet people, but you have to go to those places, put in the effort with the activities, and be open to making connections with people, and even then, that may not work, but you'll never know unless you try.
Let me give you an example from my life. In my early twenties I was lonely and I spent most of my time forum posting and chatting on IRC/AIM. I was talking to people but not making connections. An acquaintance of mine who had a lot more friends and connections suggested that perhaps I was spending too much time forum posting and chatting and not enough actually out doing things. I resisted this change for about a year, but I found that continuing to do what I was doing wasn't changing my situation. I decided to make a change in my life and to start pursing interests and connections. Weekday, I would go to work (which required me to be online as a computer programmer), but then to limit my online time at home and make an effort to go out and meet people. I didn't go out every night, but I spent some time away from the screen - I got better at cooking, I started reading more, and I focused on discovering new interests.
In some cases, this was having a drink (not necessarily an alcoholic one if you're not into alcohol) in a bar during a football game to meet other football fans. Another was to go bowling once a week which turned into joining a league. Another was to go to a farmer's market to pick up fresh vegetables. The last was joining a local Linux users group. Starting all of these activities, engaging in them with the mind of being social, coupled with learning about myself, led to both personal and professional connections being made - I met my wife, I met a future employer and hopefully startup co-founder, and I met friends that I still bowl with to this day. It was my desire to go to these events, to be open, to talk to people who were open to being talked to, and to meet regulars and connect with them that helped me move forward. I don't want to make it sound like it was all sunshine and roses - it left me tired, some of the activities I tried left me physically sore because I wasn't really fit enough for them, some of the people I met ended up being terrible people and I had to learn to cope with that/cut them out, and I had a few failed relationships along the way which bruised my heart. None of that would have happened if I just stayed on forums and chat and never made an effort to change. There is also the chance that I wouldn't have met people out and doing this, but I never would have had the opportunity if I hadn't tried.
> It's like telling an obese person to go exercise. It is meaningless advice.
If someone is obese and asks for advice on how to become more healthy then suggesting exercise (along with some exercises they can get started with - see above for my analogous answer to that) is not meaningless. If someone is obese, asks you for advice, you give them advice, they don't follow it, and then they complain about how things aren't changing and that it was meaningless that you gave them advice then the obese person might bear some responsibility for their situation not changing.
> And even more in boomer style "just take your printed CV to McDonalds to get a job" pulling people offline might be just cutting the only social link most of them have, instead of leveraging it.
Anyone that is suggesting that you go _completely_ offline is wrong - I am not suggesting that at all! You cannot go _completely_ offline and be productive, educated, and social these days. Many of the social opportunities that I mentioned above these days are organized online, so you will need to be online in some cases to know when they're happening and to keep in contact with the people you meet there. What people are suggesting is that you limit the amount of time you spend online outside of work and the necessary time to find these activities, learn about them, and maintain the connections you make while doing them.