Why is it so hard to get waves through the earth and ocean?
That's a great example of a misleading factoid; it might be true but you don't have a planet-sized ohm-meter and trying to generalise it leads you in the wrong direction.

Recall the behaviour of resistors in parallel: the wider the parallel is (more resistors), the less the overall resistance is.

Consider soldering 12 resistors together as a cube (example).  The resistance will be lower than the resistance of an individual resistor. Now extend that example by duplicating it and filling space with resistor cubes, until you have filled an earth-sized space. This is Resistorworld.

By choosing a particular value for the individual resistors you can make the resistance across Resistorworld 300 ohms. You can observe that the current takes all possible paths, of which there are a vast number. However, the paths are not of equal length. That means that you can apply a signal to one part of Resistorworld, and "see" an impedance of 300 ohms at the injection point, but trying to get it out again at a distant point you get a billion different weak signals with different arrival times, so the signal is smeared away into undetectability.