I've been on reddit for ~12 years, for example, and after five or six years still hadn't really cultivated any kind of 'group' or relationship with anyone, so I just started rotating my accounts regularly because the social aspect of the platform is essentially of zero value. HN feels much more like a community, and some of the forums I frequent are even more so, despite being largely undiscoverable and frosty to newcomers.
I won't even touch on the idea/harm of replacing physical connections with purely online ones. A lot of my friends are people I have met via the internet, but our friendships have often been cemented by eventually meeting up in person. I suspect the same is true for most people who talk about their extensive online social graph.