Some travel insurance companies refer to a "black list" or "white list" of covered travel suppliers. What does this mean?

Travel insurance is designed to cover “unforeseen” reasons. Some carriers maintain a list of covered suppliers that is referred to by some as a white list. Other insurance carriers maintain a list of suppliers that are not covered, sometimes referred to as a black list. The black lists represent circumstances with certain travel suppliers that are no longer considered unforeseen. The cancellation reasons that would not be considered for these suppliers usually relate to foreseen financial default or strike.