Probably because of spending 4+ years of school training for it, tens of thousands or even more on said schooling, and a decade or more of your life after honing those skills on the job? It’s not an easy thing for all of us to just throw away.
not quite. sunk cost implies that the cost, despite not creating any returns, is to high to throw it away.
sure, if i have no job, and i am broke, then almost anything else will do. however, switching into a new line of work is only feasible if it does not require years before i can earn enough to feed my family. as long as there is a chance at finding a job with my current skills, that pays enough, taking on such a risk doesn't make sense, unless i can actually afford doing so. in any other case my energy is better spent looking for jobs doing what i already know, where i can earn enough.
I guess the unknown is how much the market for tech jobs has dried up - will you always be able to find one? Whenever I see families in line at a food bank, I always wonder what happened that led them to that situation. I will say that employment in tech has felt like an ever-accelerating treadmill of skills that seem more akin to fashion than real technical progress; I don't think I can keep on that treadmill forever.
the unknown is how much the market for tech jobs has dried up
yes, that is the real challenge. the best thing to do would probably be to learn something new, while looking for jobs for your current experience. but balancing that can be tricky, especially if learning something new involves some kind of commitment to a training institution.