The exclusion of dust is a high priority, and the joint must be carefully tested. Once the cable has been laid and buried, the ground along the path of the cable is smoothed over, and conditions returned as closely as possible to the way they were before. Once grass grows back, it is often very difficult to tell where the cable goes. The extent of coaxial cable routes in Australia is less than the extent of microwave systems. There are many factors which come into this decision.
Coaxial cable is also vulnerable to being cut by digging or farm machinery.
These factors and many others, are taken into consideration when planning a new broadband link. Radio links are used where long distances must be covered with few intervening drop-off points. Of course, all other factors being equal, the relative costs of the systems is the determining factor. You will notice that there is often the possibility of sending traffic over two alternative paths between two places. There are many other examples.