It can be explained from three factors, bandwidth, delay and scarcity.

Bandwidth

Large communications satellites cost huge amounts of money but they can deliver coverage over wide areas pretty much irrespective of geography. Their biggest issue when compared to fiber optics is that they have a very limited bandwidth in comparison. A satellite might only occupy a couple of GHz of radio spectrum, one fiber with DWDM multiplexer could deliver the equivalent of all the bandwidth of every traditional satellite in operation.
 

The problem with optical fiber is that it is point-to-point, a satellite can broadcast information to millions of people in parallel with no more effort than to deliver to one person. But for fiber optic to reach millions of people it must be physically dragged to each person. A fiber roll-out to a population is hugely expensive but the investment once made is more flexible and powerful than satellite.

 

Satellite's biggest downfall after limited bandwidth is latency time. Data sent through a satellite has to travel much further than through a fiber. The distance from Earth to the satellite and back creates delays which make real-time communication more difficult than by fiber.

 

If you run out of capacity on a fiber, it is not a difficult task to lay another. Satellites are much harder to get permission to launch, and there are not that many usable geostationary orbits left.

So nowadays you can see more and more fiber optics cables are laid in the sea to provide the convenient communication for the world.