There are a few factors that you are overlooking. A lot of startups (and small companies) aren't on the 'SV Unicorn Track', particularly so for startups focused on 'hard' problems. Energy, biotech, aerospace, etc.. These types of startups often have to cobble together funding from a variety of sources (grants, strategic partnerships/investments, niche VC firms). The pay is lower because it has to be, funding is limited and developing the product (and sometimes just a prototype) can take years, so there is little to no revenue.

Something to consider as well, is that while the salaries might be lower, they are often not that far off from what one would make in their respective industry. So someone working at a biotech startup will probably be making a lot less than a FANNG engineer, but would probably be pretty competitive with their peers in 'BigBiotechCo'.

And the other thing to consider is that engineers, and in particular programmers, tend to be pretty bad negotiators. Its possible that your co-workers would gladly take a 30% raise if they knew they were making that much less. I highly doubt they are 'trust fund kids' (those folks tend to found crappy startups, cause if you are set for life, why would you work for someone else?). And if they are older (as you imply) its also possible they were starting to feel the impacts of ageism in tech, and took a low ball offer as a result. Or perhaps they have saved up enough from previous jobs and just don't care that much if they are maximizing their pay, and are more focused on working on cool things and with non-toxic co-workers!