I've actually found conferences quite useful for intellectual networking, although I'm not really an outgoing person, and it's not my personally preferred approach. I'd rather have some robust mailing-list communities, but they don't exist in all areas, and many people pay relatively scant attention to mailing lists. I do do most follow-up and collaboration over the internet, but in a number of cases with people I met at conferences.
In particular, I've found showing up at conferences to be a way to get your research onto people's radar who didn't previously know about it. Just by being there, and especially if you also give a talk, it can make people think of you as part of the X Research Field, and remember that you did some research on Y. In turn they're then more likely to engage with it, cite it, mention it to others when it's relevant, and maybe keep you in mind as someone to potentially collaborate with (if research interests align). All that could happen completely passively, by putting your paper on the internet and hoping people find it in a Google Scholar keyword search. But that's relatively low-probability. You could also try to approach people online, but "cold-emailing" people about research often ends up neglected, since people get a lot of email. Conferences by comparison give a setting where people are expecting to hear some talks and exchange short "what I'm working on" pitches over coffee or dinner.
I think it might even be true outside academia. Some startup/tech events are very focused on business/career networking, but others, like SuperHappyDevHouse, are great for intellectual networking.
Use conferences to make connections and get inspirations and recommendations from talking to other researchers in your field.
Being present + papers > papers.