Our habits and routines makes us what and who we are and how we act. They also make our personalities.
A Habit or routine exists because of the elements it's made from.
Elements usually are:
and even more....
But the most habits and routines have at least the elements mentioned above within themselves.
In order to change a habit or routine you only have to change one of these elements. If greater change is desired more elements can be changed. But that's not always necessary.
The problem with habits and routines is that they suck up most of our energy. To break a routine means that energy will be freed, energy that you can use for something else.
So, the main reason why people can't change is because they're stuck. Their vital energy is gate keeping those habits and routine.
Personally I don't really like self-help books because they make you "think" about acting. Although they can be motivating but very little people really change from those books.
Some people read many self-help books and the only things they can do is advice others. You can gain lots of knowledge by reading but knowledge only becomes power when you use it.