Yeah, I got into it from the TalkOrigin.org website, and 1) I'd never have gotten into it otherwise, no question, and 2) I think it took years and many, many attempts to go from "huh they refer to a talk.origins 'newsgroup' where all this fun discussion comes from, oh the link does something weird nvm" to "OH HEY I MANAGED TO SIGN UP THIS THING IS REAL WHODATHUNK".
I said that in another comment but I think discoverability is huge. The way people find things out on the internet is by going to their usual internet places or asking questions of a search engine. I don't know how people got onto Usenet in the before times but definitely at the time I got onto it everyone was on the WWW and there were very few ways to even hear about Usenet there, let alone hear something enticing enough to want to check it out. And when you combine that with the technical barrier to entry that's pretty fatal.