Perfect write-up. My sentiments exactly. And thanks for expanding on the "how this happens".
I transitioned quickly from the startup-culture to enterprise and find it a better fit, but let's talk about what you're writing:
1. I think that the customer-facing stuff is what draws the crowds in, but outside of that, a lot of people just don't give "bigger stuff" a thought. They're not put in front of a problem, hell, most people don't even know what the "problem" is. Including me. Even if I wanted to help, I don't know where to start and how I could create a one-man operation to somehow contribute. I haven't seen, to my knowledge, any open source projects that dealt with "making a change" as opposed to creating a nice set of icons.
2. Identification is definitely an issue, as I've said. We just don't know what the problems are. As a young person (hopefully still classified as that), I see the problems right in front of me, the 1st-world problems of having trouble finding friends, not knowing how to get into specific hobbies, having trouble remembering my grocery list, budgeting, sending anon hot pics to some stranger etc. Basically stuff that's been solved, and reinvented (though not perfectly) by hundreds of companies. Having been in programming for the past 3 years, I see SOME problems worth solving, but I'm not sure how to approach them.
3. The thing about "meaningful" work is that, there must be a way to do it open source, have people take part in it, contribute and get together on it, and even do it quickly. Not just in the big leagues: healthcare, water etc. No single person can get in on that, and companies that are in it are in it for the long haul. As a developer, i wouldn't want to touch that. It's years of work with potentially no results. Customer-facing stuff can take off right away. My wish is to find a sweet spot.
4. Good point. No idea what those companies are whatsoever. I'd love to read about more companies like that though.
As far as healthcare. I feel like that's a ticking time bomb. There are too many regulations to just jump in, too many slowly moving entities, and too many companies with a high stake in the game to oust you. In the tech field (the tech for the sake of tech), people use each other's ideas and evolve quickly to keep up and better themselves, no matter who they are and without ego (somewhat).
All in all, I wish the problems could be laid out, and people could work on it. I work with education stuff in my day job, and I see the issues, and as part of my job we try to solve the problems. Which is wonderful but it's difficult to identify the problems even if you work with them every day. It's easy to say "shit's broken", it's more difficult to say "here's where it's broken" and even worse to say, "find me a solution, and it'll be fixed".