It is in human nature to be afraid of, or at least hesitant to, change.  However, with job dissatisfaction at such a high level, it is surprising how many people are opposed to making a career change.  Glenn Llopis, of forbes.com, suggests there are five reasons professionals remain complacent and dormant in their careers.
The first “stuck factor” Llopis refers to is avoiding change.  Changing jobs is known to be one of the top three most stressful experiences a person can go through.  However, remaining in a job you dislike can also cause stress, so while changing jobs may temporarily create more immediate stress, remaining in that less-than-ideal job is causing long-term stress of disliking what you do 40+ hours a week.
The second “stuck factor” is resisting career progression.  This can also relate to being afraid of change, but may also require more introspection than purely avoiding change.  Progression requires a new skill set to build and once you have perfected your skill set necessary to do your current job it will tempt you to remain there.  The “Why fix what is not broken” mentality comes into play here.  But just because it isn’t broken doesn’t mean you can’t upgrade!
Llopins goes into further details about more “stuck” factors and how to progress through them.  The article, “5 Reasons People Stay Stuck in Their Careers,” is an excellent piece to read to truly manage your career.