... Because it's not an environment for learning anything. If they put you on a new project, expect to know very little of how to accomplish it, and even less of what the end result should be. There's a lack of project management in nearly all aspects of the company, and very few people can say they know exactly what they are supposed to be doing.
Fully expect to give ideas and have them taken away from you with no actual credit given. Quite a bit of work will often be overlooked, no matter how good it is.
There's also a huge communication barrier between employees. Asking for help is pointless, and is just a waste of time as you won't get it. Even basic questions are often gone unanswered. Some will use terms and acronyms that nobody else has ever heard of, but they fully expect you to know them. Some just can't speak English that well, so you'll be struggling to figure out what they're saying more than working on what needs to be done. There are many levels of inner circles, some even existing within the same department which makes it highly difficult to finish projects in a timely manner, and making it even more difficult to figure out what's supposed to be going on.
In addition, there are plenty of times where unrealistic goals are set. Such that you could never achieve them in the time limit provided. And also expect the line in the contract "other duties as required," to be used with extreme prejudice. The chances of just doing "your job" are slim to none.