Resistance to change.
That is the major driver behind ignorance, poor management etc.
Chapter 30 of Peopleware 2nd Edition is devoted to this topic. And it quotes from a book by another fairly well known consultant, written a bit earlier though:
And it should be considered that nothing is more difficult to handle, more doubtful of success, nor more dangerous to manage, then to put oneself at the head of introducing new orders. For the introducer has all those who benefit from the old orders as enemies, and he has lukewarm defenders in all those who might benefit from the new orders.
Niccolo Machiavelli: The Prince (1513)
DeMarco and Lister go on stating the mantra to keep in mind before asking people to change:
The fundamental response to change is not logical, but emotional.
The process of change is rarely a straight and smooth drive from the current suboptimal conditions to the new, improved world. For any nontrivial change, there is always a period of confusion and chaos before arriving to the new status quo. Learning new tools, processes and ways of thinking is hard, and takes time. During this transition time productivity drops, morale suffers, people may complain and wish if only it was possible to return to the good old ways of doing things. Very often they do, even with all the problems, because they feel that the good ol' known problems are better than the new, unknown, frustrating and embarrassing problems. This is the resistance which must be tactfully and gently, but decidedly overcome in order to succeed.
With patience and perseverance, eventually the team arrives from Chaos to the next stage, Practice and Integration. People, although not completely comfortable with the new tools/processes, start to get the hang of these. There may be positive "Aha" experiences. And gradually, the team achieves a new status quo.
It is really important to realize that chaos is an integral, unavoidable part of the process of change. Without this knowledge - and preparation for it -, one may panic upon hitting the Chaos phase, and mistake it with the new status quo. Subsequently the change process is abandoned and the team returns to its earlier miserable state, but with even less hope of ever improving anything...
For reference, the phases described above were originally defined in the Satir Change Model (named after Virginia Satir).