Generally programmers working at those companies don't know about or don't care about HN.
This has always been the case for humanity, that typically people who do challenging, high salary work come from wealthier families with access to better resources, including better social signaling resources to enable them to stand out from the pack.
It's just part of the game; if you want to play at the top without being born into it, you have a long way to climb, and you are competing against everyone else in your position. You have to either meet the filtering criteria, or find a way to stand out from the crowd.
Btw, you don't need to create an OSS project from scratch. You could also get visibility by making important contributions to an existing one.
Pretty much, yes.