Just one perspective: I'm a web developer who's mostly worked in solar and environmental nonprofits for the last decade.
My salary has been anywhere from $32k to $98k (briefly), with no equity of any sort, pretty bad healthcare, limited vacation, terrible mid management, etc. I was happy with those jobs because they felt socially benevolent in some small way, but it's a lot less money than what you'd get working for a proper tech company that took investor money and spent it on ad tech or whatever.
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And many of those problems you cited aren't predominantly software issues to begin with. I think devs have this idea that good tech can fix anything, but it's not really true in the real world.
Recycling isn't a software problem, for example, but a market forces one. It's cheaper to just make most things new, and really expensive to dispose of them properly now that Asia doesn't want as much of our shit. It was never really economically viable, but for a while we were able to just dump our shit on third world countries to pretend like it was going away.
Clean energy is a growing sector but there isn't much software work, and much of it is outsourced to cheaper countries. Where there is software, it's often pretty niche (like solar mapping, design, rooftop layouts, etc.) that are graphics and Canvas heavy on the web stack, which isn't what most web devs specialize in. There is also firmware engineering but only a few companies in that space, and most of them aren't in the US anymore.
Education suffers from academic inertia (it's very slow to change and management heavy with business minded admins who don't care about student experience as much as making a profit), political battles, angry parents, and weaponized school boards. Those people usually don't care much about the tech.
Healthcare and biotech are growing too, but it's extremely difficult to get anything to market because of patents and regulatory hurdles. FDA approval is a pain. Not something solo hackers and small companies can easily tackle, and also hard to build a moat around before big pharma or Fitbit or whatever decides to copy you.
I mean, if you give the average developer the choice of a niche field working on stuff where they won't really make a difference anyway, for a third of the pay or less, while limiting their networks and career opportunities... vs just going to work for a mainstream tech company, well, it's a pretty easy choice for most.