When you are still employed in your current job, it can be rather intimidating to apply for a different position even if, in the long run, it matches your plans for the future more closely. In your current position you can perform many tasks intuitively and without much effort. A new position means uncertainties - colleagues, clients and supervisors are strangers. Thus, most employees prefer to stay with their current employer even though they are dissatisfied.
Despite the desire for personal and financial development, many will remain in their old position to protect themselves from anything new.
This behavior is also known as the "Boiled Frog Syndrome". A frog sits in a pot of water, which is slowly brought to a boil. Although the water becomes more and more uncomfortable, the frog stays put. Eventually it's too late to get out...
In the professional world factors such as the need to always be up-to-date (especially in the technology sector) define only very short timeframes for career advancement. It is crucial to be aware of this.