A brothel?! Geez.
This particular operation involved illegal immigrants, but whether we talking about illegal citizens or just criminal citizens that are here legally, I take it as a sign of importance that zoning laws are enforced.
It's kind of like how there's no such thing as a routine traffic stop. All the stuff about the number of unrelated people living in a house, number of cars in the driveway, etc. can help law enforcement snuff out bigger stuff like this.