[btoptical]

A fiber is point-to-point unless there's an add/drop along the way. A submarine cable is point-to-point between say California and Japan or New York and Southampton.

That 5GHz radio has short reach and low capacity. It'd only make sense in certain situations. It would not be suitable for the gigantic capacity required by the Internet backbones.

For example, with the advent of coherent optical technology, you typical submarine cable is carrying 4000x the capacity of that radio (4Tb/s). Terrestrial long haul systems can be easily 8Tb/s.