What is the name of the phenomenon where a person abandons simplifying a complex system upon understanding the system?
The phenomenon may be explained like this :


The programmer was given the task to fix a bug on a complicated legacy code he does not understand.
The programmer forms a subgoal "Refactor the code", in order to achieve the above goal.
In the process of achieveing the subgoal "Refactor the code", he understands what needs to be done to fix the bug. So the refactoring is not a useful goal any more and it is abandoned.


So we have a primary goal of fixing the bug and a secondary goal, formed to serve the primary goal, to refactor the code. When the primary goal is achieved the secondary is no longer relevant.

To promote refactoring you must take actions so that the secondary goal of refactoring becomes also a primary goal, concurrently with other tasks like fixing a bug. For example you may give rewards to programmers that successfully refactor the code or you may change the culture of your team, so that refactoring is considered a social norm, etc.