[Aser]

A quick bit of research shows that the speed of light in air only 0.3% less than the speed of light in a vaccuum. So that works out to 298,896km/s. This is significantly faster than the speed of light in an fibre optic cable (around 200,000km/s). Combine this with the ability for a microwave link to have a shorter path than optical fibre, and it's easy to see why a microwave link can be lower latency.

Nobody is disputing the fact that fibre optic can handle much higher bandwidths, but that is irrelevant in this application. The amount of data required to make a trade is probably in the order of kiloBytes or MegaBytes, easily handled by the few Gbps limit of microwave links.

The reason why satellite internet is so terrible is because a geostationary satellite sits 22,236 miles above the surface of the earth. So for a roundtrip journey, a packet of data has to travel nearly 45,000 miles.