The economics of certain resources are such that the cost of retrieving them is not worth what they're worth. Indeed, wishful thinking guides much of the economy. While any money spent is arguably in hopes of some type of return, some returns are more feasible than others. From fossil fuels to minerals to whale oil, history has plenty of examples of this.
It also may be applied to military history. Some regions are simply so poor, so backwards, and so remote, influencing control there is harder than it's worth. This is why rural Afghanistan was, is, and will be among the world's backwaters. Even chasing fugitives into such territory may not necessarily be worth it. Some people likewise have little worth stealing. Perhaps insuring that all are poor means that there is little left to steal.