HOLLARD TRAVEL INSURANCE - Cancellation - difference in insurable risk

I have just spent over an hour, between calling their Call Centre twice, and carefully going through the wording of their travel insurance policy, which we want to take for cancellation BEFORE we leave on a scheduled, expensive, bucket-list trip to Zimbabwe later this year that their policy does NOT cover self-drive, "because of the difference in insurable risk".

Please can someone explain to me why, if I fly to a destination or drive to a destination, in a neighbouring country, the insurable risk for cancellation BEFORE the trip would be different? And their cover is therefore not applicable/cannot be purchased because we are driving, and not flying?

Amazing - NOT!