Well it is not up to me to justify the nature of the world! It just does. But you are not the first person to be surprised at the speed.
The speed of any wave results from the rapidity with which an oscillation of one thing or in one region is passed on to the neighbouring thing or region. This speed is affected by two things
- The strength of the springiness that pulls the thing back from its disturbed state (e.g. the tension in the duct tape which twisted the kebab sticks back).
- The inertia of the thing moving (e.g. whether jelly babies are on the end of the kebab sticks or not.
To make a wave fast you need (a) very big restoring forces and (b) very light masses. When we think of space, we can appreciate the very light masses, but not where the strong restoring forces come from. I say ‘that’s just how it is’ but I am sure someone somewhere is trying to work out the properties of space that make light travel so fast through it.