True, but what percentage of software engineers work on those?

The only pool of software that both employs a large number of engineers, has an engineering life measured in decades and isn't rewritten every 3-5 years to a large degree is enterprise software, in my experience. Think C/C++/Java/.NET middleware type stuff.

And I imagine 90% of HN actively runs away from those jobs :-)

I wouldn't know. But I imagine there's an availability bias.

I've worked in more 'traditional' engineering fields (manufacturing, energy, healthcare, aerospace) and the vast, vast majority are long tenured systems built for dedicated systems. For those in SV, I imagine it's the opposite.