The answers to this point are mostly right. The author is saying that short lived neighborhoods with unstable populations don't allow for the formation of "organized crime".
I suppose it's true. The problem we have here, is that while it's probably true, it has no rational point. It's like explaining that the streets run north and south and east and west, because people like the sunrise and sunset. Yeah, we admire sunrises and sunsets, and some towns have streets that align with the compass points. But there is no logical connection between them.
The argument is saying that transient populations in financially and otherwise unstable neighborhoods offer few opportunities to get rich in organized crime. One has to wonder what they're advocating. What's the link between the two statements? What IS the point of the argument? Transience and instability prevent crime? Or it's bad because it decreases financial opportunity through organized crime?
I suspect that this is a game of semantics, and used to support a rather pointless theory - that being that social structure existing in a neighborhood CAUSES, or at least FOSTERS, organized crime. The authors could not possibly be advocating for tearing down social order and/or social interaction on an ordered basis, nor could they possibly be advocating the chaotic dysfunctional neighborhood as an answer to crime. The statement, in my mind, is met with a "so what? Do you have some point to this exercise?" question.
One can easily understand your confusion at reading it. I had to google a while to gain some context on the authors and statement to make heads or tails of it myself.