Ignorance of the poor is chosen
The comfortable don't know how the poor live because they don't care to, not because the facts are hidden. As long as those below can be held in place, those on top have no reason to look.
The comfortable look only under pressure
Those on top start asking what is wrong only when crowding and misery below grow bad enough to cause violent unrest. Their inquiry is a response to trouble that can no longer be ignored, not a sudden fit of conscience.
Neighbors living in another country
Rich and poor in the same city can be so cut off from each other that the poor might as well live in a foreign land. Their housing becomes a marker of a social divide that refuses to close.
Bad housing breeds crime and sickness
Crime, drink and disease among the poor follow from the overcrowded, badly built buildings they are forced into, not mainly from their own weak character. Fix the dwelling and you treat the cause rather than the symptom.