[Terr_]

I think it has to do with the timing and history of the internet, which carried a bunch of correlated groups (not just those two) forward together.

Both are fairly niche groups with no real geographic concentration. When someone can't cast around for a local club in town, the internet becomes a game-changer for finding the far-flung and diffuse others in the group. Then once you've found those other people (and related furry/security media to consume/publish) computers are again the way to get anything done, as opposed to snail-mail, phone calls or physical travel.