It's not clear how high the barrier to entry to software is; if the barrier is low, we can expect wages to drop, long-term. People are (reportedly) getting six figure jobs from a six week bootcamp, which could be troubling to people getting paid only somewhat higher for 20 years of experience. And since remote work is clearly here to stay, why would companies hire for US salaries when they could hire somewhere else in the world for less?
There's also concern about whether the stack I have experience with will be around in five years (particularly bad in the Web arena), concern about will I be able to get a job after I'm forty, concern about will I be able to get a job if I have to whiteboard leetcode exercises, etc.
Plus, if you have a mortgage in a high cost of living area (likely if you are in tech) with a family of four, say, your burn rate is pretty high, which is fear-inducing. How long can you afford to pay a $1 million mortgage with no job? Even if you think you will probably be okay, there is a non-negligible (with unknown probability) that you might not find a job and, say, lose your house. There is a potentially huge tail-risk in switch jobs. So even if the market is good in general, there is a risk that if it is not good for you there might be a disaster. On top of this, you read about plenty of layoffs when the economy turns poor, so you know the company is not likely to care about your personal situation. Whether or not the situation is actually precarious, the risk makes you feel like it is.
(In my case, freelancing has been helpful for the fears, because you look for work so much more frequently, and your perspective on your work options, and even what you are selling changes.)
