1 - Lack of variety, leading to boredom. After decades in the industry, I'm super bored with the things I know, and not in the least bit interested in learning more technical minutia of whatever flavor... pretty much all of it feels the same. The things I'm still interested in (like Scheme) are pretty obscure, so I'm unlikely to ever get to work with them. I hate all the mainstream tech stacks, but that's where the overwhelming majority of work is.
2 - I don't care about what the company does. 99.9% of the time, the real goal is to make some extremely rich people even richer. Couldn't care less. I'm not sure that even if I worked for a non-profit doing work I thought was important that it would translate to my own job being something I wanted to do.
3 - Chronic understaffing, crazy time pressure, and lack of resources. This is endemic in the tech field. Count yourself incredibly lucky if you don't have to face this day in and day out for years on end. It's even worse when you know the company you're working for is making money hand over fist and they could easily afford to hire more people, treat them better, and get more resources, but you know they'd rather funnel that money in to the pockets of those at the top.
4 - Lies and corporate BS. From bullshit cheerleading and pep talks from upper management that a child would be stupid to believe, to time wasting, useless policies, to outright lying and two-facedness that's super common in the industry. Who wants to deal with this?
5 - Depression. This doesn't help.
The best job I ever had was working part time in a tiny company where it was just me and the owner. He was a super nice guy, we got along great and just did what needed to be done. No corporate BS, no policies, no lies, and back then I wasn't burnt out yet, so working on tech stuff still seemed interesting.
After burning out on tech I really should have switched to another career (completely outside of tech)... or even tried management, but I never did, and my skills have atrophied so I'm super rusty and out of it regarding the newer buzzword technologies.. though I'd like to think that I still have good troubleshooting skills and can learn anything.. if I cared.. but I don't.