I've recently been reading/watching a lot about towns that have been abandoned. In some cases, these are towns in countries with population decline, but most prominently, these are towns that relied on a single industry that went away. A typical one in the US is coal mining.
It occurred to me that this is a manifestation of Bus Factor 2 but one level of granularity up. Instead of a project depending on one key person, you have a town dependent on one industry. These towns often enjoyed a lot of prosperity when the industry was booming due to their specialisation, but then declined as fast as they boomed when that one industry went away.
My claim: a town needs at least two diverse industries to survive this sort of trap!