This exaggerates the range over which the rivers in question move. They aren't regularly destroying houses and other buildings that need broadband. Rather, they

This exaggerates the range over which the rivers in question move. They aren't regularly destroying houses and other buildings that need broadband. Rather, they take various paths through low land that is already devoted to the passage of rivers. Rivers on alluvial plains are more movable than rivers in mountain gorges, but they pose no greater threat to cables than they do to other permanent facilities like roads, buildings, power lines, etc. Even in the rare cases when a section of cable must be replaced, it's still just plow it into deep soil rather than bore through rock the whole way.