Pff, it's because we're in a field that values cranking out mediocre code fairly fast over writing solid code that will continue to function forever. Young people are much more likely to spend 60 hour weeks working on some program, and that's what they want.
The only reason I still am very employable is that I look much younger than my age, and I shaved off a decade from my resume. It doesn't hurt that I am constantly on the new, new thing (though I just can't do it with AI, because the LLM's code is so, so terrible, and a lot of AI programming jobs actually have no programming at all!) and it doesn't hurt that I have a huge collection of very high quality open-source libraries.
Many people I know my age or younger have simply been sidelined, and it's horrible for them.
In other engineering fields, senior engineers are highly valued. Perhaps this is why so many software projects fail when so very few bridges or buildings collapse during construction...
Interesting article, accept several claps!!