Think I know why. Personally very satisfied with my IT job (but not living in the US). But I wanted to do computer science and got what I wanted.
I see a lot of collegues even at good companies (including some people working at Google in California) that went into IT through a life accident. It was bright, they were promised fame and money, and they got in.
Guess what ? It didn't work out exactly like that.
First they discovered that tech hierarchy is essentially flat. While at most jobs you might go up the corporate ladder with a lot of steps (you don't gain that much power but you can say you were promoted), Tech company have like 4 levels of hierarchy. So either, you stand out or you'll stay at the start. To stand out, you have to "live, breathe and eat this stuff" (seen at an industry tradeshow). And on top of that, you need social skills. If you are not able to "eat live and breath this stuff", don't come into IT. If you love this but don't have social skills, you'll have to be really amazing. The focus on efficiency as a core value means that if you are not really good, you'll be treated as "replacable".
Second, you might be considered a wizard in your hometown, but once you are in "premiere league", then you are just a developper. And you might not be as good as you previously tought. Every kid, knowing how to use a computer used to be venerated as "a genius". And well, it wasn't that hard to fix a computer. If you come working at Google, Twitter or any other tech company either you are very good and will work on prime stuff or you'll be paid to refactor code or other menial tasks. At all tech companies, you have the elite who define the infrastructure, they are very few, very well paid, and usually happy. But if you're not good enough to do that, you end up, using infrastructure other developped or worse, as a code janitor.
Then, there's the value stuff. Well these companies do have values. They are those of the technical society (read Jacques Ellul to know better) which means : No values escept efficiency. Or, if it's more efficient, do it regardless of the consequences. I know more than one people at Google that were not easy with this. Most of them were outsiders from the tech fields. And they quickly were not at ease when they discovered when discussing with senior level people who where in transhumanist or other kind of geek dreams. In these companies either you dream if changing the world by making it more efficient or you are not considered to have a leading mindset. This is not a written set of values of course, but it is essentially that : Uber does not make it for values, or even money, they target the most efficient way to change the taxi industry. And it will take what it takes to achieve it. Society however favors people who make things efficient, so you get money doing it even if you are not after money. That's why you have companies with no business models : They know if they make things more efficient, money will come, so money is not a goal. Humanistic values are not a goal either. If you find pleasure in solving problems, making things efficient and watching how powerful you are then tech work is for you. If not, you should avoid tech companies.
NB : And the worst is working in tech for a non tech company, then nobody understand nobody.