I think a major component of the difference between contributing then and contributing now is friction/skill/interest. Back then, you had to be specifically interested in learning how to get connected, which was a niche endeavor, while the masses were oblivious or too cool for school. Now, you can simply join almost any online community using baseline skills that an enormous fraction of Earth's population already has.

Artificially constructing a similar level of friction/gatekeeping would have major downsides that might not be worth it, but it could theoretically achieve a community that behaves as that past one did, if that's the goal. Sort of a CAPTCHA to prove you're not just a human, but a leet one. As others have said, HN achieves this in a way. Perhaps non-tech communities can do a similar thing. But educational materials to slowly penetrate the barrier must exist.