The false assumption here is that people are naturally inclined to do nothing unless given money.

In the situation you describe, I would have a pretty strong motivation to fix the problem if it was my property (deeply unpleasant living conditions). If it was my neighbor's property, I would also have a strong motivation to fix it (sense of community). Neither of those things is tied to money.

Not everyone is motivated by the same things. Avarice is not the root of all industry.