Could you please explain more? Finding people online and discovering they live hundreds of miles away generally feels isolating to me, even potentially increasing the sense of isolation I feel from just the failed local friendships.

Sure. I think this is simply an idiosyncratic aspect of our personalities. While you find those online people who might be friends but live far away feels isolating, I find that getting to know the people who read and comment on my blog over months and years (sometimes we email back and forth) creates a real bond, much like like the epistolary friendships of the nineteenth century conducted only by mail between people who never actually met IRL. Some of my daily readers have been commenting for 15-20 years!