Walking, hiking, paddle boarding, skiing, biking on recreation paths all have existed for years. People can choose to do activities that have normal social interaction. Or not. Don't blame a particular economic system.
It's funny that in your examples you entirely chose excercise.
The point is that it used to not be a choice. Most people were constantly socialising because their work involved lots of socialising, and their housing was shared with lots of people. Those things are a lot less prevalent than they used to be.
At school it's very easy to make friends not just because you're a kid or that you're choosing to socialise, but just by default you spend 6+ hours a day with the same people.
Life has choices.