I can only surmise, but I have thought about this same question every time I end up in an engineering department that turns "IT" underneath me -- it has happened a couple of times now. I have left both times, after making attempts to push the organization back the other way hard enough to be threatened with termination.
People make this choice because they have convinced themselves they never had a choice. They remain there because they are convinced they still don't have a choice.
The explanation is usually a story of falling or being forced into a position followed by stating the tautology of it being a job. They are willing to take a painful known quantity over an unknown quantity elsewhere -- which is assumed to be at least as painful --, all the while saying to themselves repeatedly "I need to be stronger than the pain for the people who rely on me." Sometimes this will become even more self-fulfilling, and they will assume they have no other options, painful or not.
Along with this, they will provide rationalizations about how, even if they had a choice, it really would not matter. The purpose of a job is money. Full stop. If you make it anything else, you are martyring yourself to your employer. Thus, it doesn't matter where you work, so long as you are. Any desire you have to make those hours of your day more meaningful need to be bottled away, because they never will be. Those who don't accept this are ignorant of the facts of life, which are assumed to be true by means of circular logic and a desire to rationalize one's own rut in life.
Humans are amazingly good at rationalization, even when it starts from the usually faulty premise that where they are now is the best things can possibly get.
Hope this provides some insight about your question.