I would argue that President Johnson spent most of his time on the Vietnam War, rather than on domestic policy, because it was more obviously pressing. It may also have been that he felt that the outcome of the war would do more to determine what his legacy was than any of his domestic programs would.
It is not surprising that a president would spend more time on foreign affairs in this situation. Many people in the US at the time believed that the security of the country would truly be diminished by a communist victory in Vietnam. If Johnson truly believed this, it would make sense for him to prioritize the war. Poverty or other such domestic issues would not be as dangerous to the country and were therefore less important. In addition, the war was causing the deaths of Americans in very obvious ways. This would catch a president’s attention more than the less visible problems caused by poverty.
In addition to this, Johnson may have been thinking about his legacy. He would not have wanted to be known as the president who lost a war. Therefore, he would have worried about the war more than about domestic issues.