- Most of my career was made by being the author of one popular open source platform which happened to do well.
- I've recruited people based on open-source contributions. If I want an expert in [X], finding someone who contributed to [X] is a good bet.
- The flip side is I've made (minor, helpful) contributions to many projects in part for exposure. My name is in the commit list of many systems in domains where I have wanted to work.
- Many mid-sized contributions look good on a resume, especially for a junior developer. Indeed, I've made one case to promote someone based, in part, on contributing to a library we were using (even if only tangentially).
If you want a job in e.g. network security, find something in a firewall, anonymzing proxy, packet sniffer, or whatnot, and make a PR. It's often quick, easy, and helpful. A corollary is you do actually learn a lot about a system by contributing.
I have no axe to grind here, but I think the cynicism is unwarranted.
That's more a salesperson mantra than SWE, where for every 10-100 people you ask, someone buys something. However, I've raised money many times simply by shamelessly asking.
Second good life lesson: Don't assume things about others.
People who make $1/day, $10/day, $100/day, $1000/day, $10,000/day, etc. have fundamentally different priorities and motivations. Ditto on many other axes. Good synergies are leveraged working across such differences.