Earlier quoted context omitted.
On the flip side? As somebody who has plenty of open source projects--the set of employers who actually looks at them is within epsilon of zero. I have not once, not once gotten a meaningful question from anything I have posted on Github in any interview or client meeting even after suggesting up-front that it's worth taking a look. And I used to interview on a monthly basis just to keep in practice! No--instead you…
You must be applying to the wrong companies then. I just got done doing interviews, and I looked at what the second round candidates had available on GitHub and their personal site, and the one who got the job had about 5 projects that were impressive. Good employers care. I care. Its not signaling. Its important.
It's not important. There are plenty of good companies who don't do these things that manage to pay developers $100k salaries. They may assess in other ways, but it's not the only signal.
It's only important to you. You choose what you want to see in candidates. You need buy-in from the candidates that your process is conducive to a good environment, good code, and good delivery. In turn, you cultivate a team who share something in common, and the team gets along well and makes good code.
It's people finding like-minded people -- the same social movements that are in every other profession. There's nothing wrong with it, but there's currently no prevailing right or wrong way to do it, otherwise that would be the technical interview.
Practically, development is still in demand. So if I get rejected, I can go apply some place else. That's why it's not important.
Maybe your pay is slightly above those other companies, but is a marginal pay increase really worth all of the extra effort? That's up to the developer. But the employers that don't use this criteria are not non-good employers.