[eck]

It moves at that speed because the index of refraction of glass is about 1.5. In single-mode fiber the light doesn't really bounce off the walls.

[sgt101]

Also significant latency is imposed by the network architecture vs the choice of bearer, and by shared vs single user. My guess is that the main driver is actually to get a private channel with qos guarantees and as few retransmission hops and security bumps as possible.