But all of the media people and politicians were on Twitter, and not on Bob's auto parts forum.

You read HN; you're not a normal person. 95% of everyone you know didn't hear about the Hunter Biden thing at the time, and most of them probably still don't know about it.

That's utter rubbish. Plenty of people with high follower counts were talking about it, as were right wing followed of the former President.

The story was still up on the NY Post website.

Exactly: the vast majority of people don't use Twitter and aren't part of anyone's "follower count".

Most people outside of your (and my) bubble don't read the news, don't pay much attention to politics, aren't particularly well educated, don't think very hard about who they're going to vote for (if they even vote), and if they use Twitter at all it's to post cat videos and keep up with the Kardashians.

You might not cross paths with this kind of person much in your daily life, but I promise you they're everywhere - and most of them would struggle to tell you what Joe Biden's son's name is, let alone what controversies he's been involved in.